In the theory of relativity, it is convenient to express results in terms of a spacetime coordinate system relative to an implied observer. In many (but not all) coordinate systems, an event is specified by one time coordinate and three spatial coordinates. The time specified by the time coordinate is referred to as coordinate time to distinguish it from proper time.

In the special case of an inertial observer in special relativity, by convention the coordinate time at an event is the same as the proper time measured by a clock that is at the same location as the event, that is stationary relative to the observer and that has been synchronised to the observer's clock using the Einstein synchronisation convention.

For non-inertial observers, and in general relativity, coordinate systems can be chosen more freely. For a clock whose spatial coordinates are constant, the relationship between proper time Failed to parse (Missing texvc executable; please see math/README to configure.): \tau

, i.e. the rate of time dilation, is given by

Next Time (sometimes rendered "Некст Тајм" in Macedonian Cyrillic) is a rock duo from Skopje, Republic of Macedonia. The duo consists of twin brothers Martin and Stefan Filipovski. Stefan fronts the band as the lead singer, while Martin plays the guitar and sings back-up vocals. The group represented Macedonia at the Eurovision Song Contest 2009 in Moscow, Russia but failed to reach the final.

Next Time was formed in early 2008 after they signed with Plan B Production. Previously they performed as a garage band at children's music festivals. Discovered by composer and songwriter, Jovan Jovanov, the Macedonian duo released their first single "Ne Veruvam Vo Tebe" ("I Don't Believe in You") in May, 2008. The song's lyrics were written by Next Time with Jovanov as the producer. "Ne Veruvam Vo Tebe" immediately topped a number of charts in Macedonia and was quickly a hit which shot Next Time through the roof of the Macedonian music scene.^{[citation needed]} The band also released their first music video for the song. Next Time's first festival appearance was at the First Radio Music Festival "Zvezdena Nok" in June, 2008. At "Zvezdena Nok", the duo won the "Summer Hit of the Year" award with their second song "Me Mislish Li?" ("Am I In Your Thoughts?"). Two months later at Ohrid Fest, Next Time were voted "Best New Artist" with their third single "Me Ostavi Sam Da Zhiveam" ("You Left Me All Alone"). Next Time's biggest festival success came in October when they won the second semi-final at MakFest. With their fourth single "Bez Tebe Tivko Umiram" ("I'm Slowly Dying Without You") they went on to finish second in the final, only three points behind the winner.