[[Image:DaylightSaving-World-Subdivisions.png|upright=1.67|thumb|alt=World map. Europe, Russia, most of North America, parts of southern South America and southern Australia, and a few other places use DST. Most of equatorial Africa and a few other places near the equator have never used DST. The rest of the land mass is marked as formerly using DST.| Although not used by most of the world's people, daylight saving time is common in the Northern Hemisphere high latitudes. ]]

Daylight Saving Time (DST)—also summer time in most countries including in British English and European official terminology (see ''Terminology'')—is the practice of temporarily advancing clocks during the summertime so that afternoons have more daylight and mornings have less. Typically clocks are adjusted forward one hour near the start of spring and are adjusted backward in autumn. Modern DST was first proposed in 1895 by George Vernon Hudson. Many countries have used it since then; details vary by location and change occasionally.

The practice has been both praised and criticized. Adding daylight to afternoons benefits retailing, sports, and other activities that exploit sunlight after working hours, but causes problems for farming, evening entertainment and other occupations tied to the sun. Its effect on health and crime is less clear. Although an early goal of DST was to reduce evening usage of incandescent lighting, formerly a primary use of electricity, modern heating and cooling usage patterns differ greatly, and research about how DST currently affects energy use is limited or contradictory.

DST clock shifts present other challenges. They complicate timekeeping, and can disrupt meetings, travel, billing, recordkeeping, medical devices, heavy equipment, and sleep patterns. Software can often adjust computer clocks automatically, but this can be limited and error-prone, particularly when DST protocols are changed.

Origin

[[Image:Clepsydra-Diagram-Fancy.jpeg|thumb|upright|alt=A water clock. A small human figurine holds a pointer to a cylinder marked by the hours. The cylinder is connected by gears to a water wheel driven by water that also floats, a part that supports the figurine.| In this ancient water clock, a series of gears rotated a cylinder to display hour lengths appropriate for each day's date.]]

Although not punctual in the modern sense, ancient civilizations adjusted daily schedules to the sun more flexibly than modern DST does, often dividing daylight into twelve hours regardless of day length, so that each daylight hour was longer during summer. For example, Roman water clocks had different scales for different months of the year: at Rome's latitude the third hour from sunrise, ''hora tertia'', started by modern standards at 09:02 solar time and lasted 44 minutes at the winter solstice, but at the summer solstice it started at 06:58 and lasted 75 minutes. After ancient times, equal-length civil hours eventually supplanted unequal, so civil time no longer varies by season. Unequal hours are still used in a few traditional settings, such as some Mount Athos monasteries and all Jewish ceremonies.

During his time as an American envoy to France, Benjamin Franklin, author of the proverb, "Early to bed, and early to rise, makes a man healthy, wealthy and wise", anonymously published a letter suggesting that Parisians economize on candles by rising earlier to use morning sunlight. This 1784 satire proposed taxing shutters, rationing candles, and waking the public by ringing church bells and firing cannons at sunrise. Franklin did not propose DST; like ancient Rome, 18th-century Europe did not keep precise schedules. However, this soon changed as rail and communication networks came to require a standardization of time unknown in Franklin's day.

Modern DST was first proposed by the New Zealand entomologist George Vernon Hudson, whose shift-work job gave him leisure time to collect insects, and led him to value after-hours daylight. In 1895 he presented a paper to the Wellington Philosophical Society proposing a two-hour daylight-saving shift, and after considerable interest was expressed in Christchurch, New Zealand he followed up in an 1898 paper. Many publications incorrectly credit DST's invention to the prominent English builder and outdoorsman William Willett, who independently conceived DST in 1905 during a pre-breakfast ride, when he observed with dismay how many Londoners slept through a large part of a summer's day. An avid golfer, he also disliked cutting short his round at dusk. His solution was to advance the clock during the summer months, a proposal he published two years later. The proposal was taken up by the Liberal Member of Parliament (MP) Robert Pearce, who introduced the first Daylight Saving Bill to the House of Commons on 12 February 1908. A select committee was set up to examine the issue, but Pearce's bill did not become law, and several other bills failed in the following years. Willett lobbied for the proposal in the UK until his death in 1915.

Starting on 30 April 1916, Germany and its World War I allies were the first to use DST () as a way to conserve coal during wartime. Britain, most of its allies, and many European neutrals soon followed suit. Russia and a few other countries waited until the next year and the United States adopted it in 1918. Since then, the world has seen many enactments, adjustments, and repeals.

Procedure

[[Image:Begin CEST Transparent.png|thumb|upright=0.67|alt=Diagram of a clock showing a transition from 2:00 to 3:00.| When DST starts in central Europe, clocks advance from 02:00 CET to 03:00 CEST.]]

In a typical case where a one-hour shift occurs at 02:00 local time, in spring the clock jumps forward from 01:59 standard time to 03:00 DST and that day has 23 hours, whereas in autumn the clock jumps backward from 01:59 DST to 01:00 standard time, repeating that hour, and that day has 25 hours. A digital display of local time does not read 02:00 exactly at the shift, but instead jumps from 01:59:59.9 either forward to 03:00:00.0 or backward to 01:00:00.0. In this example, a location observing UTC+10 during standard time is at UTC+11 during DST; conversely, a location at UTC−10 during standard time is at UTC−9 during DST.

Clock shifts are usually scheduled near a weekend midnight to lessen disruption to weekday schedules. A one-hour shift is customary, but Australia's Lord Howe Island uses a half-hour shift. Twenty-minute and two-hour shifts have been used in the past.

Coordination strategies differ when adjacent time zones shift clocks. The European Union shifts all at once, at 01:00 UTC; for example, Eastern European Time is always one hour ahead of Central European Time. Most of North America shifts at 02:00 local time, so its zones do not shift at the same time; for example, Mountain Time can be temporarily either zero or two hours ahead of Pacific Time. In the past, Australian districts went even further and did not always agree on start and end dates; for example, in 2008 most DST-observing areas shifted clocks forward on October 5 but Western Australia shifted on October 26. In some cases only part of a country shifts; for example, in the U.S., Hawaii and most of Arizona do not observe DST.

Start and end dates vary with location and year. Since 1996 European Summer Time has been observed from the last Sunday in March to the last Sunday in October; previously the rules were not uniform across the European Union. Starting in 2007, most of the United States and Canada observe DST from the second Sunday in March to the first Sunday in November, almost two-thirds of the year. The 2007 U.S. change was part of the Energy Policy Act of 2005; previously, from 1987 through 2006, the start and end dates were the first Sunday in April and the last Sunday in October, and Congress retains the right to go back to the previous dates now that an energy-consumption study has been done.

Beginning and ending dates are the reverse in the southern hemisphere. For example, mainland Chile observes DST from the second Saturday in October to the second Saturday in March, with transitions at 24:00 local time. The time difference between the United Kingdom and mainland Chile may therefore be five hours during the Northern summer, three hours during the Northern winter and four hours a few weeks per year because of mismatch of changing dates.

Western China, Iceland, Russia and other areas skew time zones westward, in effect observing DST year-round without complications from clock shifts. For example, Saskatoon, Saskatchewan, is at longitude, slightly west of center of the idealized Mountain Time Zone , but the time in Saskatchewan is Central Standard Time year-round, so Saskatoon is always about 67 minutes ahead of mean solar time. Conversely, northeast India and a few other areas skew time zones eastward, in effect observing negative DST. The United Kingdom and Ireland experimented with year-round DST from 1968 to 1971 but abandoned it because of its unpopularity, particularly in northern regions.

Western France, Spain, and other areas skew time zones and shift clocks, in effect observing DST in winter with an extra hour in summer. For example, Nome, Alaska, is at longitude, which is just west of center of the idealized Samoa Time Zone , but Nome observes Alaska Time with DST, so it is slightly more than two hours ahead of the sun in winter and three in summer. Double daylight saving time has been used on occasion; for example, Britain used it during World War II.

DST is generally not observed near the equator, where sunrise times do not vary enough to justify it. Some countries observe it only in some regions; for example, southern Brazil observes it while equatorial Brazil does not. Only a minority of the world's population uses DST because Asia and Africa generally do not observe it.

Dispute over benefits and drawbacks

Willett's 1907 proposal argued that DST increases opportunities for outdoor leisure activities during afternoon sunlight hours. The longer days nearer the summer solstice in high latitudes offer more room to shift daylight from morning to evening so that early morning daylight is not wasted. DST is commonly not observed during most of winter, because its mornings are darker: workers may have no sunlit leisure time, and children may need to leave for school in the dark.

General agreement about the day's layout confers so many advantages that a standard DST schedule usually outranks ad hoc efforts to get up earlier, even for people who personally dislike the DST schedule. The advantages of coordination are so great that many people ignore whether DST is in effect by altering their nominal work schedules to coordinate with television broadcasts or daylight.

Energy use

DST's potential to save energy comes primarily from its effects on residential lighting, which consumes about 3.5% of electricity in the U.S. and Canada. Delaying the nominal time of sunset and sunrise reduces the use of artificial light in the evening and increases it in the morning. As Franklin's 1784 satire pointed out, lighting costs are reduced if the evening reduction outweighs the morning increase, as in high-latitude summer when most people wake up well after sunrise. An early goal of DST was to reduce evening usage of incandescent lighting, formerly a primary use of electricity. Although energy conservation remains an important goal, energy usage patterns have greatly changed since then, and recent research is limited and reports contradictory results. Electricity use is greatly affected by geography, climate, and economics, making it hard to generalize from single studies. The U.S. Dept. of Transportation (DOT) concluded in 1975 that DST might reduce the country's electricity usage by 1% during March and April, but the National Bureau of Standards (NBS) reviewed the DOT study in 1976 and found no significant savings. In 2000 when parts of Australia began DST in late winter, overall electricity consumption did not decrease, but the morning peak load and prices increased. In Western Australia during summer 2006–07, DST increased electricity consumption during hotter days and decreased it during cooler days, with consumption rising 0.6% overall. Although a 2007 study estimated that introducing DST to Japan would reduce household lighting energy consumption, a 2007 simulation estimated that DST would increase overall energy use in Osaka residences by 0.13%, with a 0.02% decrease due to less lighting more than outweighed by a 0.15% increase due to extra cooling; neither study examined non-residential energy use. DST's effect on lighting energy use is noticeable mainly in residences. A 2007 study found that the earlier start to DST that year had little or no effect on electricity consumption in California. A 2007 study estimated that winter daylight saving would prevent a 2% increase in average daily electricity consumption in Great Britain. This paper was revised in October 2009 . A 2008 study examined billing data in Indiana before and after it adopted DST in 2006, and concluded that DST increased overall residential electricity consumption by 1% to 4%, due mostly to extra afternoon cooling and extra morning heating; the main increases came in the fall. The overall annual cost of DST to Indiana households was estimated to be $9 million, with an additional $1.7–5.5 million for social costs due to increased pollution. The U.S. Dept. of Energy (DOE) concluded in a 2008 report that the 2007 U.S. extension of DST saved 0.5% of electricity usage during the extended period. This report analyzed only the extension, not the full eight months of daylight saving, and did not examine the use of heating fuels.

Several studies have suggested that DST increases motor fuel consumption. The 2008 DOE report found no significant increase in motor gasoline consumption due to the 2007 U.S. extension of DST.

Economic effects

Retailers, sporting goods makers, and other businesses benefit from extra afternoon sunlight, as it induces customers to shop and to participate in outdoor afternoon sports. In 1984, ''Fortune'' magazine estimated that a seven-week extension of DST would yield an additional $30 million for 7-Eleven stores, and the National Golf Foundation estimated the extension would increase golf industry revenues $200 million to $300 million. A 1999 study estimated that DST increases the revenue of the European Union's leisure sector by about 3%. Conversely, DST can adversely affect farmers and others whose hours are set by the sun. For example, grain harvesting is best done after dew evaporates, so when field hands arrive and leave earlier in summer their labor is less valuable. DST also hurts prime-time broadcast ratings, drive-ins and other theaters.

Changing clocks and DST rules has a direct economic cost, entailing extra work to support remote meetings, computer applications and the like. For example, a 2007 North American rule change cost an estimated $500 million to $1 billion. Although it has been argued that clock shifts correlate with decreased economic efficiency, and that in 2000 the daylight-saving effect implied an estimated one-day loss of $31 billion on U.S. stock exchanges, the estimated numbers depend on the methodology and the results have been disputed.

Public safety

In 1975 the U.S. DOT conservatively identified a 0.7% reduction in traffic fatalities during DST, and estimated the real reduction to be 1.5% to 2%, but the 1976 NBS review of the DOT study found no differences in traffic fatalities. In 1995 the Insurance Institute for Highway Safety estimated a reduction of 1.2%, including a 5% reduction in crashes fatal to pedestrians. Others have found similar reductions. Single/Double Summer Time (SDST), a variant where clocks are one hour ahead of the sun in winter and two in summer, has been projected to reduce traffic fatalities by 3% to 4% in the UK, compared to ordinary DST. It is not clear whether sleep disruption contributes to fatal accidents immediately after the spring clock shifts. A correlation between clock shifts and traffic accidents has been observed in North America and the UK but not in Finland or Sweden. If this effect exists, it is far smaller than the overall reduction in traffic fatalities. A 2009 U.S. study found that on Mondays after the switch to DST, workers sleep an average of 40 minutes less, and are injured at work more often and more severely.

In the 1970s the U.S. Law Enforcement Assistance Administration (LEAA) found a reduction of 10% to 13% in Washington, D.C.'s violent crime rate during DST. However, the LEAA did not filter out other factors, and it examined only two cities and found crime reductions only in one and only in some crime categories; the DOT decided it was "impossible to conclude with any confidence that comparable benefits would be found nationwide". Outdoor lighting has a marginal and sometimes even contradictory influence on crime and fear of crime.

In several countries, fire safety officials encourage citizens to use the two annual clock shifts as reminders to replace batteries in smoke and carbon monoxide detectors, particularly in autumn, just before the heating and candle season causes an increase in home fires. Similar twice-yearly tasks include reviewing and practicing fire escape and family disaster plans, inspecting vehicle lights, checking storage areas for hazardous materials, reprogramming thermostats, and seasonal vaccinations. Locations without DST can instead use the first days of spring and autumn as reminders.

Health

[[Image:Greenwich GB DaylightChart.png|upright=1.67|thumb| alt=Graph of sunrise and sunset times for 2007. The horizontal axis is the date; the vertical axis is the times of sunset and sunrise. There is a bulge in the center during summer, when sunrise is early and sunset late. There are step functions in spring and fall, when DST starts and stops.| Clock shifts affecting apparent sunrise and sunset times at Greenwich in 2007]]

DST has mixed effects on health. In societies with fixed work schedules it provides more afternoon sunlight for outdoor exercise. It alters sunlight exposure; whether this is beneficial depends on one's location and daily schedule, as sunlight triggers vitamin D synthesis in the skin, but overexposure can lead to skin cancer. Sunlight strongly influences seasonal affective disorder. DST may help in depression by causing individuals to rise earlier, but some argue the reverse. The Retinitis Pigmentosa Foundation Fighting Blindness, chaired by blind sports magnate Gordon Gund, successfully lobbied in 1985 and 2005 for U.S. DST extensions, but DST can hurt night blindness sufferers.

Clock shifts disrupt sleep and reduce its efficiency. Effects on seasonal adaptation of the circadian rhythm can be severe and last for weeks. A 2008 study found that although male suicide rates rise in the weeks after the spring transition, the relationship weakened greatly after adjusting for season. A 2008 Swedish study found that heart attacks were significantly more common the first three weekdays after the spring transition, and significantly less common the first weekday after the autumn transition. The government of Kazakhstan cited health complications due to clock shifts as a reason for abolishing DST in 2005. Dmitri Medvedev, president of Russia, had claimed that health risks as a product of DST were the motivation for Russia to nullify DST.

Complexity

DST's clock shifts have the obvious disadvantage of complexity. People must remember to change their clocks; this can be time-consuming, particularly for mechanical clocks that cannot be moved backward safely. People who work across time zone boundaries need to keep track of multiple DST rules, as not all locations observe DST or observe it the same way. The length of the calendar day becomes variable; it is no longer always 24 hours. Disruption to meetings, travel, broadcasts, billing systems, and records management is common, and can be expensive. During an autumn transition from 02:00 to 01:00, a clock reads times from 01:00:00 through 01:59:59 twice, possibly leading to confusion.

Damage to a German steel facility occurred during a DST transition in 1993, when a computer timing system linked to a radio time synchronization signal allowed molten steel to cool for one hour less than the required duration, resulting in spattering of molten steel when it was poured. Medical devices may generate adverse events that could harm patients, without being obvious to clinicians responsible for care. These problems are compounded when the DST rules themselves change; software developers must test and perhaps modify many programs, and users must install updates and restart applications. Consumers must update devices such as programmable thermostats with the correct DST rules, or manually adjust the devices' clocks.

Some clock-shift problems could be avoided by adjusting clocks continuously or at least more gradually—for example, Willett at first suggested weekly 20-minute transitions—but this would add complexity and has never been implemented.

DST inherits and can magnify the disadvantages of standard time. For example, when reading a sundial, one must compensate for it along with time zone and natural discrepancies. Also, sun-exposure guidelines like avoiding the sun within two hours of noon become less accurate when DST is in effect.

Politics

Daylight saving has caused controversy since it began. Winston Churchill argued that it enlarges "the opportunities for the pursuit of health and happiness among the millions of people who live in this country" and pundits have dubbed it "Daylight Slaving Time". Historically, retailing, sports and tourism interests have favored daylight saving, while agricultural and evening entertainment interests have opposed it, and its initial adoption had been prompted by energy crisis and war.

The fate of Willett's 1907 proposal illustrates several political issues involved. The proposal attracted many supporters, including Balfour, Churchill, Lloyd George, MacDonald, Edward VII (who used half-hour DST at Sandringham), the managing director of Harrods, and the manager of the National Bank. However, the opposition was stronger: it included Prime Minister Asquith, Christie (the Astronomer Royal), George Darwin, Napier Shaw (director of the Meteorological Office), many agricultural organizations, and theater owners. After many hearings the proposal was narrowly defeated in a Parliament committee vote in 1909. Willett's allies introduced similar bills every year from 1911 through 1914, to no avail. The U.S. was even more skeptical: Andrew Peters introduced a DST bill to the U.S. House of Representatives in May 1909, but it soon died in committee.

After Germany led the way with starting DST () during World War I on 30 April 1916 together with its allies to alleviate hardships from wartime coal shortages and air raid blackouts, the political equation changed in other countries; the United Kingdom used DST first on 21 May 1916. U.S. retailing and manufacturing interests led by Pittsburgh industrialist Robert Garland soon began lobbying for DST, but were opposed by railroads. The U.S.'s 1917 entry to the war overcame objections, and DST was established in 1918.

The war's end swung the pendulum back. Farmers continued to dislike DST, and many countries repealed it after the war. Britain was an exception: it retained DST nationwide but over the years adjusted transition dates for several reasons, including special rules during the 1920s and 1930s to avoid clock shifts on Easter mornings. The U.S. was more typical: Congress repealed DST after 1919. President Woodrow Wilson, like Willett an avid golfer, vetoed the repeal twice but his second veto was overridden. Only a few U.S. cities retained DST locally thereafter, including New York so that its financial exchanges could maintain an hour of arbitrage trading with London, and Chicago and Cleveland to keep pace with New York. Wilson's successor Warren G. Harding opposed DST as a "deception". Reasoning that people should instead get up and go to work earlier in the summer, he ordered District of Columbia federal employees to start work at 08:00 rather than 09:00 during summer 1922. Many businesses followed suit though many others did not; the experiment was not repeated.

Since Germany's adoption in 1916 the world has seen many enactments, adjustments, and repeals of DST, with similar politics involved. The history of time in the United States includes DST during both world wars, but no standardization of peacetime DST until 1966. In the mid-1980s, Clorox (parent of Kingsford Charcoal) and 7-Eleven provided the primary funding for the Daylight Saving Time Coalition behind the 1987 extension to U.S. DST, and both Idaho senators voted for it based on the premise that during DST fast-food restaurants sell more French fries, which are made from Idaho potatoes. In 1992 after a three-year trial of daylight saving in Queensland, Australia, a referendum on daylight saving was held and defeated with a 54.5% 'no' vote - with regional and rural areas strongly opposed, while those in the metropolitan south-east were in favour. In 2005, the Sporting Goods Manufacturers Association and the National Association of Convenience Stores successfully lobbied for the 2007 extension to U.S. DST. In December 2008, the Daylight Saving for South East Queensland (DS4SEQ) political party was officially registered in Queensland, Australia, advocating the implementation of a dual-time zone arrangement for Daylight Saving in South East Queensland while the rest of the state maintains standard time. DS4SEQ contested the March 2009 Queensland State election with 32 candidates and received one percent of the state-wide primary vote, equating to around 2.5% across the 32 electorates contested. After a three-year trial, more than 55% of Western Australians voted against DST in 2009, with rural areas strongly opposed. In the UK the sport and leisure industry supports a proposal to observe SDST's additional hour year-round. On 14 April 2010, after being approached by the Daylight Saving for South East Queensland (DS4SEQ) political party, Queensland Independent member Peter Wellington, introduced the Daylight Saving for South East Queensland Referendum Bill 2010 into Queensland Parliament, calling for a referendum to be held at the next State election on the introduction of daylight saving into South East Queensland under a dual-time zone arrangement. The Bill was defeated in Queensland Parliament on 15 June 2011.

Terminology

Although ''daylight saving time'' is considered to be correct, ''daylight savings time'' is commonly used. The form ''daylight saving time'' uses the present participle ''saving'' as an adjective, as in ''labor saving device''; the first two words are sometimes hyphenated, as in ''daylight-saving time''. The common variants ''daylight savings time'' and ''daylight savings'' use ''savings'' by analogy to ''savings account''. ''Daylight time'' is also common. Willett's 1907 proposal used the term ''daylight saving'', but by 1911 the term ''summer time'' replaced ''daylight saving time'' in draft legislation in Britain, and continental Europe uses similar phrases, such as ''Sommerzeit'' in Germany, ''zomertijd'' in Dutch, ''horario de verano'' or ''hora de verano'' in Spain and ''l'heure d'été'' in France, whereas in Italy the term is ''ora legale'', that is, legal time.

The name of local time typically changes when DST is observed. American English replaces ''standard'' with ''daylight'': for example, ''Pacific Standard Time'' (''PST'') becomes ''Pacific Daylight Time'' (''PDT''). British English calls UK time ''British Summer Time'' (BST), and typically inserts ''summer'' into other time zones, e.g. ''Central European Time'' (''CET'') becomes ''Central European Summer Time'' (''CEST''). Abbreviations do not always change: for example, many (though not all) Australians say that ''Eastern Standard Time'' (''EST'') becomes ''Eastern Summer Time'' (also ''EST''). In Australia it is also called EDT (Eastern Daylight Time)

The American English mnemonic "spring forward, fall back" (also "spring ahead ...", "spring up ...", and "... fall behind") helps people remember which direction to shift clocks. Much of North America now advances clocks before the vernal equinox, so the mnemonic disagrees with the astronomical definition of spring, but a proposed substitute "March forward ..." works only in the northern hemisphere, and is less robust against future rule changes.

Computing

[[Image:Daylightsavings.svg|thumb|upright| alt=Strong man in sandals and with shaggy hair, facing away from artist, grabbing a hand of a clock bigger than he is and forcing it backwards. The clock uses Roman numerals and the man is dressed in stripped-down Roman gladiator style. The text says "You can't stop time... But you can turn it back one hour at 2 a.m. on Oct. 28 when daylight-saving time ends and standard time begins."| A 2001 U.S. public service advertisement reminded people to adjust clocks manually.]]

Changes to DST rules cause problems in existing computer installations. For example, the 2007 change to DST rules in North America required many computer systems to be upgraded, with the greatest impact on email and calendaring programs; the upgrades consumed a significant effort by corporate information technologists. Some applications standardize on UTC to avoid problems with clock shifts and time zone differences.

Many systems in use today base their date/time calculations from data derived from zoneinfo, which is sometimes known as tzdata.

Tz database

The tz database maps a name to the named location's historical and predicted clock shifts. This database is used by many computer software systems, including most Unix-like operating systems, Java, Mac OS X and Oracle; HP's "tztab" database is similar but incompatible. When temporal authorities change DST rules, zoneinfo updates are installed as part of ordinary system maintenance. In Unix-like systems the TZ environment variable specifies the location name, as in TZ='America/New_York'. On Linux however there is a system-wide setting that is applied if the TZ environment variable isn't set, this setting is controlled by the contents of the /etc/localtime file, which is usually a symlink or hardlink to one of the zoneinfo files. Internal time is stored in timezone-independent epoch time; the TZ is used by each of potentially many simultaneous users and processes to independently localize time display.

Older or stripped-down systems may support only the TZ values required by POSIX, which specify at most one start and end rule explicitly in the value. For example, TZ='EST5EDT,M3.2.0/02:00,M11.1.0/02:00' specifies time for eastern North America starting in 2007. TZ must be changed whenever DST rules change, and the new TZ value applies to all years, mishandling some older time stamps.

Microsoft Windows

As with zoneinfo, a user of Microsoft Windows configures DST by specifying the name of a location, and the operating system then consults a table of rule sets that must be updated when DST rules change. Procedures for specifying the name and updating the table vary with release. Updates are not issued for older versions of Microsoft Windows. Windows Vista supports at most two start and end rules per time zone setting. In a Canadian location observing DST, a single Vista setting supports both 1987–2006 and post-2006 time stamps, but mishandles some older time stamps. Older Microsoft Windows systems usually store only a single start and end rule for each zone, so that the same Canadian setting reliably supports only post-2006 time stamps.

These limitations have caused problems. For example, before 2005, DST in Israel varied each year and was skipped some years. Windows 95 used rules correct for 1995 only, causing problems in later years. In Windows 98 Microsoft marked Israel as not having DST, forcing Israeli users to shift their computer clocks manually twice a year. The 2005 Israeli Daylight Saving Law established predictable rules using the Jewish calendar but Windows zone files cannot represent the rules' dates in a year-independent way. Partial workarounds, which mishandle older time stamps, include manually switching zone files every year and a Microsoft tool that switches zones automatically.

Microsoft Windows keeps the system real-time clock in local time. This causes several problems, including compatibility when multi booting with operating systems that set the clock to UTC, and double-adjusting the clock when multi booting different Windows versions, such as with a rescue boot disk. This approach is a problem even in Windows-only systems: there is no support for per-user timezone settings, only a single system-wide setting. In 2008 Microsoft hinted that future versions of Windows will partially support a Windows registry entry RealTimeIsUniversal that had been introduced many years earlier, when Windows NT supported RISC machines with UTC clocks, but had not been maintained since.

An interesting effect can be observed with file time properties. The NTFS file system used by recent versions of Windows stores the file with a UTC time stamp, but displays it corrected to local—or seasonal—time. However, the FAT filesystem commonly used on removable devices stores only the local time. Consequently, when a file is copied from the hard disk onto separate media, its time will be set to the current local time. If the time adjustment is changed, perhaps automatically (daylight saving) or if the user selects a different time zone, then when the timestamps of the original file and the copy are compared there will be a difference. This may be verified (without having to wait for the next equinox) by copying a file, removing the media, adjusting the time zone options, reconnecting the media, and viewing the details of the file and its copy. This effect needs to be in mind when trying to determine if a file is a duplicate of another although there are other methods of comparing files for equality like using check sums algorithms.

Notes

External links

Daylight Saving Time—general history and anecdotes

:* Saving Time, Saving Energy—North American viewpoint :* Summer Time—European viewpoint

Sources for time zone and daylight saving time data—technical resources

Graphical Display of Time Differences with Daylight Saving Time (DST) Changes

ITU LEGAL TIME 2011

Information about the Current Daylight Saving Time (DST) Rules, U.S. National Institute of Standards and Technology (NIST.gov)

* When Daylight Saving Time begins in 2011 (United States)

Countries and territories operating Daylight Saving Time (2010/2011)

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Birth name	Paul Francis Tompkins
Birth date	September 12, 1968
Birth place	Philadelphia, Pennsylvania
awards	Emmy Award in writing for Mr. Show with Bob and David }}

Paul Francis Tompkins (born September 12, 1968), best known as Paul F. Tompkins, is an American actor and comedian.

Life and career

Tompkins was born in Philadelphia, Pennsylvania to a receptionist mother and railway worker father. He started out in stand-up comedy in 1986 at The Comedy Works, Philadelphia, PA, where he was half of a duo with the late Rick Roman. He moved to Los Angeles in 1994.

In what has been characterized as his first big entertainment industry job, Tompkins appeared as a featured player on ''Mr. Show with Bob and David'' and served as a staff writer for the show's second and third seasons. He also appeared in several episodes of the short-lived ''Tenacious D'' TV series and appeared in the 2006 Tenacious D film ''Tenacious D in The Pick of Destiny''.

Tompkins was a contributor on ''The Daily Show'' in 1998 doing a semi-weekly segment called ''Us People's Weekly Entertainment'', where he would poke fun at entertainment magazines. In 1998, he created ''Driven to Drink'', a one-man show that aired on HBO. He recorded two half-hour specials for the ''Comedy Central Presents'' TV series, one in 2003 and another in 2007. In the first season of ''Real Time with Bill Maher'', Tompkins had his own segment.

He began hosting VH1's Best Week Ever in its revised format in late 2008 and continued to do so until it left the air in June 2009. Tompkins has been a frequent guest on MSNBC's Countdown with Keith Olbermann and can also often be heard as a regular guest of Tom Scharpling's The Best Show on WFMU radio show.

From 2008 through 2010, Tompkins has increased his web presence by appearing as a guest for new media formats, specifically podcasts. He has had numerous appearances on various podcast episodes including ''Comedy Bang Bang'', ''The Nerdist Podcast'', ''Never Not Funny'', ''Doug Loves Movies'', ''Comedy & Everything Else'', ''The Sound of Young America'', ''Mostly Comedy'' and ''The Superego Podcast''. On the Comedy Death-Ray Radio podcast, he has been both the guest host, when regular host Scott Aukerman was away, and appeared as character impressions of actors John C. Reilly and Ice-T, and composer Andrew Lloyd Webber. In the "Best of Comedy Death-Ray Radio 2009" episode, Tompkins's impression of Ice-T on Bonus Episode 1 was voted #1 by fans of the show via Twitter.

Tompkins starred in P.T. Anderson's ''There Will Be Blood'' (2007) as a character named Prescott and in Steven Soderbergh's "The Informant!" (2009) as FBI Agent Anthony D’Angelo. Tompkins also had a small role in Anderson's ''Magnolia'' (1999) that was cut from the final film. He also performs with Aimee Mann (another frequent Anderson collaborator) in her annual Holiday Show.

His first stand-up comedy album, ''Impersonal'', was released in 2007 on AST Records. In the liner notes, Tompkins explains that the jokes on the CD are his older, less personal material. He said at the time that he would record another album in the coming year that features his more recent work. On December 1, 2009 he released this project, his second CD entitled ''Freak Wharf''.

On March 18, 2009, Tompkins appeared on Comedy Central Presents. His most recent one-hour special, entitled "You Should Have Told Me", debuted on June 11, 2010.

Tompkins frequently performs live in Los Angeles at Largo, Comedy Death-Ray, Thrilling Adventure Hour and the Upright Citizens Brigade Theatre. In 2009 he was brought to Toronto after a Facebook group found 300 Torontonians who vowed to attend if he did. This spurred like-minded fans in Halifax, Dallas, and Memphis amongst others to launch successful campaigns to lure Tompkins there.

Tompkins made guest appearances on the ''Aqua Teen Hunger Force'' episodes "Boston" and "Juggalo". He also made a guest appearance on True Jackson, VP.

Tompkins married actress Janie Haddad on April 24, 2010.

On July 31, 2010 Tompkins launched ''The Pod F. Tompkast'', a free monthly comedy podcast featuring excerpts from his show at Largo, new original sketches, and conversations with Jen Kirkman.

On October 28, 2010, Tompkins joined Mike Nelson, Kevin Murphy, and Bill Corbett in Nashville, Tennessee as a guest riffer for a Rifftrax Live event riffing on the 1959 horror movie, House on Haunted Hill. Tompkins helped riff a short, "Paper and I", and then came back briefly to help riff the feature film. The DVD release of this special was released on May 17, 2011, and the blu-ray version was released on August 2, 2011.

Discography

2007 ''Impersonal'' (Released on AST Records)

2007 ''Comedy Death-Ray'' (Compilation released on Comedy Central Records)

2009 ''Freak Wharf'' (Released on AST Records)

2010 ''Sir, You Have Fooled Me Twice'' (EP) (Released on AST Records)

Podcasts

''The Pod F. Tompkast''

''Doug Loves Movies''

''Comedy Death-Ray Radio''

References

External links

"Paul F. Tompkins, The Famous Comedian" Official Website

Paul F. Tompkins interviewed on TV show "Drinking with Ian"

2007 Interview with WickedInfo.com

Interview with Paul F. Tompkins on Public Radio International's "The Sound of Young America"

IMPOSE Magazine Interview July 2007

Toronto Star article on Tompkins

Scene Missing Magazine Interview with Paul F. Tompkins

Pod F. Tompcast

Category:1968 births Category:American comedians Category:American film actors Category:American stand-up comedians Category:American television actors Category:American television writers Category:Actors from Pennsylvania Category:Living people Category:People from Philadelphia, Pennsylvania