W-Number (depending on manufacturer, also called k-number) is the relationship between the turns of a speedometer cable for distance traveled. It depends on wheel size and the ratio to the drive shaft or drive shaft to the speedometer. The W-Number is given as a value on old mechanical speedometer, for example, "W = 715" means that 1000 meters come back down to 715 revolutions of the speedometer cable. For other manufacturers K is used here instead of W.
With electronic speedometers, as now installed as part of instrument clusters in automobiles, the K-number is often a customizable by the workshop computer service value that is stored in an EEPROM, for example. Is usually necessary if a change in the vehicle assembly or a change in tire sizes with slightly different diameters."