0-100 Fahrenheit represents about as hot and cold as it gets in a temperate environment
whose thumb? whose foot? whose armspan? whose paces, under what circumstances?
if you're accustomed to metric, there are similar everyday objects that you can use for reference, with the added advantage that you're not using an archaic system
It doesn't actually matter whose foot/thumb because you're just using quick reference.
ok. similar quick references exist for metric. ---