NOTE 1 The duration of a time interval is a non-negative quantity equal to the difference between the dates of the final instant and the initial instant of the time interval, when the dates are quantitative marks. Different time intervals may have the same duration, e.g. the period of a time-dependent periodic quantity is a duration that is independent of the choice of the initial instant.

NOTE 2 The duration is one of the base quantities in the International System of Quantities (ISQ) on which the International System of Units (SI) is based. The term “time” instead of “duration” is often used in this context and also for an infinitesimal duration.

NOTE 3 For the term “duration”, the word expressions “time” or “time interval” are often used, but the term “time” is not recommended in this sense and the term “time interval” is deprecated in this sense to avoid confusion with the concept of “time interval”.

NOTE 4 The coherent SI unit of duration and time is second, s (see IEC 60050-112). The units minute (1 min = 60 s), hour (1 h = 60 min = 3 600 s), and day (1 d = 24 h = 86 400 s) are accepted for use with the SI.

NOTE 5 In common language, the word “time” is used with several different meanings. In technical language, however, more precise terms, e.g. date, duration, time interval should be used.