5.12 Representation of time in ordinary prose and with SI units

Except in descriptive text and in approximations, write the time of day in numerical form:

  • The program will be broadcast at 8:05 p.m.


  • He said that he would call after ten o’clock.

In a scientific or technical context, express precise measurements of elapsed time by means of the internationally recognized symbols of time d for day, h for hour, min for minute and s for second:

  • h 20 min flying time
  • The test run took 1 d 3 h 43 min 09 s precisely.

These symbols should also be used when units of time are expressed with SI units:

  • 16 km/d
  • 16 m/s
  • 10 J/h
  • 60 r/min