Byr was often used in geology and astronomy as a unit of one billion years. The "b" is an abbreviation for "billion" (i.e., thousand million), with "yr" simply an abbreviation for "year". Today, the International System of Units specifies to use Ga, though Gy or Gyr may be used sometimes. Since a billion means 1000 million in the U.S. but has meant a million million in Great Britain, and still does in many non-English speaking countries, its use is discouraged. This article does not cite its references or sources. ... A giant Hubble mosaic of the Crab Nebula. ... The definition, agreement and practical use of units of measurement have played a crucial role in human endeavour from early ages up to this day. ... One thousand million (1,000,000,000) is the natural number following 999,999,999 and preceding 1,000,000,001. ... A year is the time between two recurrences of an event related to the orbit of the Earth around the Sun. ... Cover of brochure The International System of Units. ... Short scale is the English translation of the French term échelle courte, which designates a system of numeric names in which the word billion means a thousand millions. ...

See also

• Myr
• kyr