|Definition:|| system of ordered marks which can be attributed to instants on the time axis, one instant being chosen as the origin|
NOTE 1 A time scale may be chosen as:
- continuous, e.g. international atomic time (TAI) (see 713-05-18),
- continuous with discontinuities, e.g. coordinated universal time (UTC) (see 713-05-20) due to leap seconds, standard time due to summer time awinter time,
- successive steps, e.g. usual calendars, where the time axis is split up into a succession of consecutive time intervals and the same mark is attributed to all instants of each time interval,
- discrete, e.g. in digital techniques.
NOTE 2 For physical and technical applications, a time scale with quantitative marks is preferred, based on a chosen initial instant together with a unit of measurement.
NOTE 3 Customary time scales use various units of measurement in combination, such as second, minute, hour, or various time intervals of the calendar such as calendar day, calendar month, calendar year.