The hardest to convert is probably temperature.
There both a very different scale and they are harder to "see". With weight or length you can visualise and get a rough estimate if you are close. But temperature ia harder.
I have a feeling for the mesurements (don't say I'm fluent in converting, not even close) amd know if i'm close or wrong. Weight because i use never is harder but temperature is a weird one for me. 100F, hot, cold, superhot, you will burn yourself when touching something? 100C is boiling water, so don't touch hot. Same with 20F. Do i need wintergloves? Is water freezing? Can i lick it? No idea, I have to use a converter.
Ok i know that 20F is wintergear cold and 100F is very sweaty warm. But on an engine no idea what to expect.