What's the use of "pinching your fingers" in "counting your fingers"? Why are a few fingers pinching around for show or can they really play any role?

Fortune-telling needs to cooperate with heavenly stems and earthly branches, but heavenly stems and earthly branches's calculation is very troublesome. To imagine the mutual cooperation between 12 and 1, paper and pencil are generally needed, but the ancients seldom have the opportunity to use paper and pencil when calculating numerology. Therefore, divide your fingers into three sections, just fix them for twelve days, and when matching with the earthly branches, you need to read the earthly branches according to the knuckles, so that you can calculate the heavenly stems and earthly branches of the year and month more quickly.