Talk:Introduction to Geochronology/Units of Time

From http://physics.nist.gov/Pubs/SP811/sec05.html

Certain units that are not part of the SI are essential and used so widely that they are accepted by the CIPM, and thus by this Guide, for use with the SI [2, 3]. These units are given in Table 6. The combination of units of this table with SI units to form derived units should be restricted to special cases in order not to lose the advantages of the coherence of SI units. (The use of SI prefixes with the units of Table 6 is discussed in Sec. 6.2.8)

Additionally, this Guide recognizes that situations on occasion will require the use of time-related units other than those given in Table 6; such as using intervals of time be expressed in weeks, months, or years. In such cases, if a standardized symbol for the unit is not available, the name of the unit should be written out in full. (See Sec. 8.1 for a suggestion regarding the symbol for year and Chapter 9 for the rules and style conventions for spelling unit names.)

... And from http://physics.nist.gov/Pubs/SP811/sec08.html#8.1

The SI unit of time (actually time interval) is the second (s) and should be used in all technical calculations. When time relates to calendar cycles, the minute (min), hour (h), and day (d) might be necessary. For example, the kilometer per hour (km/h) is the usual unit for expressing vehicular speeds. Although there is no universally accepted symbol for the year, Ref. [4: ISO 80000-3] suggests the symbol a.

Noahmclean (discuss • contribs) 16:20, 20 March 2014 (UTC)