Years ago the UK's highway code ( much of it not a legal instrument for driving ) hand book had braking distances on th back cover expresses as car lengths and also the thinking distaance for the braking also given in car lengths.
More than amusing if you were driving a BMC mini or perhaps a big converted to RHD " Yankee tin beetle " , purchased from some USAF guy who was going back home to the state side of things.
Yet if you didn't know or couldn't repeat the distances when questioned you got an automatic fail there & then before you'd even started to drive the driving test & you were not allowed to do the driving , the test was over right there & then.
In truth there is not great problem working in different bases / units of measurement , once you start playing with several on a regular basis they soon become second nature .