Gregory's ServerI hope this isn't rude, but to bounce off your post, a few years ago I saw an article about using one hand to count to 12, which I found amazing.
You use your thumb to point to the different joints of the fingers, with index tip being one, middle top being two, all the way to the joint closest to the hand on the little finger being 12.
It also allows for the other hand to count multiples of 12 each time you "wrap round", but that requires more mental arithmetic.
@DuvetGecko @vincent @CppGuy I haven't heard of this but I do have a book I haven't read yet called The Complete Book of Fingermath, that supposedly helps you learn how to do fairly complex calculations using just your fingers:
https://archive.org/details/completebookoffi0000lieb