What year did the speedometer in cars change from mph to kph?

Interesting question and many not so interesting answers so far. In the UK, it is required that your speedometer is calibrated in mph but for nearly all analogue dials (ie with background and pointer) there are km markings too for the benefit of those to travel abroad. Ironically in the rest of the EU we only get km calibration so when we drive into the UK we do not have mph markings and have to constantly recalculate the speed limits. Not so difficult as 160 kph = 100 mph, 80 kph = 50 mph etc etc. One exception to all this is where you have digital instruments and you can set both the speedometer and the odometer to record in miles or kms.
==============
kia cars|used honda