BIMP/JCGM, Vocabulaire international de métrologie (VIM) / International vocabulary of metrology, 2008 (JCGM 200:2012), 1.9
For a particular quantity, many different units may be used. For example, the speed v of a particle may be expressed in the form v = 25 m/s = 90 km/h, where the metre per second and kilometre per hour are alternative units for expressing the same value of the quantity speed.