Metrology is the science of measurement. Metrology includes all theoretical and practical aspects of measurement. The word comes from Greek μέτρον (metron), "measure" + "λόγος" (logos), amongst others meaning "speech, oration, discourse, quote, study, calculation, reason". In Ancient Greek the term μετρολογία (metrologia) meant "theory of ratios".

Metrology is defined by the International Bureau of Weights and Measures (BIPM) as "the science of measurement, embracing both experimental and theoretical determinations at any level of uncertainty in any field of science and technology." The ontology and international vocabulary of metrology (VIM) is maintained by the International Organisation for Standardisation.

Metrology is a very broad field and may be divided into three subfields:

A core concept in metrology is metrological traceability, defined by the BIPM as "the property of the result of a measurement or the value of a standard whereby it can be related to stated references, usually national or international standards, through an unbroken chain of comparisons, all having stated uncertainties." The level of traceability establishes the level of comparability of the measurement: whether the result of a measurement can be compared to the previous one, a measurement result a year ago, or to the result of a measurement performed anywhere else in the world.

Carl Zeiss (11 September 1816 – 3 December 1888) was a German maker of optical instruments commonly known for the company he founded, Carl Zeiss Jena (now: Carl Zeiss AG). Zeiss made contributions to lens manufacturing that have aided the modern production of lenses. Raised in Weimar, Germany, he became a notable lens-maker in the 1840s when he created high-quality lenses that were "wide open", or in other words, had a very large aperture range that allowed for very bright images. He did this in the city of Jena at a self-opened workshop, where he started his lens-making career. At first his lenses were only used in the production of microscopes, but when cameras were invented, his company began manufacturing high-quality lenses for cameras.

Zeiss began his life in pre-imperial Germany where he went to a grammar school, and undertook apprenticeship under Dr. Friedrich Körner, mechanic and supplier to the court. He later attended lectures in mathematics, experimental physics, anthropology, mineralogy and optics at the University of Jena. After seven years he opened a small workshop with hardly any tools. He made many lenses but had little recognition until 1847 when he hired his second and third apprentice.

John Neal (August 25, 1793–June 20, 1876), was most notably an author and art/literary critic. He was also a man of diverse talents and objectives, many of which were pioneering in his day. For example, he is credited as being the first American author to employ colloquialism in his writing, breaking with more formal traditions in literature. However, he was also undisciplined and often rambling, so despite its period significance, his literary work has drifted into obscurity. He was also an early women's rights advocate, prohibitionist, temperance advocate, opponent of dueling, accomplished lawyer, boxer, and architect.

Born in a yellow frame house on Free Street at the corner of South Street in Falmouth (now Portland, Maine) of Quaker parents, he attended school until the age of twelve whereupon he entered into business. For nine years he made a living as haberdasher, clerk, dry goods dealer, traveling penmanship tutor, and miniature artist, among other things, before entering law school in Baltimore, Maryland in 1815. Neal supported himself while in school by writing for local periodicals, and he helped found a literary society, The Delphian Club. Neal wrote for and eventually edited the journal the Delphians created—a short-lived but influential and admired monthly journal titled The Portico. In short time, he turned to novels and poetry, publishing some six novels and two epic poems (under the pseudonymous 'clubicular' name, "Jehu O'Cataract," a nickname given to him by the Delphians because of his rapid production). He was proud of the speed with which he threw off his volumes, often taking only a week to finish an entire novel. He wrote during this stage in his life that, "I shall write, as others drink, for exhilaration." Neal left for England in late 1823.