there was an attempt to change this (in France) to 400 gradians (grads) to create a metric measure
once 360 degrees is established, the various fractions can be determined
this work is intended to be quick and, ideally, mental
what are the angles shown?
I failed to make a note of the source and couldn't find it again ... (?)
more (mental) work can focus on angles between numbers on the clock face and between the compass points