I heard that this method has been known since the Vedic age. It might has been known much longer (we can’t decipher Indus script yet).

You can count between 0 and 15 (0 to F in hex) on one hand or between 0 and 255 (00 to FF in hex) on two hands.

A horizontal move to the neighboring finger on the left adds or subtracts 4 (depending on which direction you move); while the same move on the right hand adds/subtracts 40 in hex (assuming that your count the least significant digit on the left and the most significant digit on the right; you can do the other way around as well).

For example, lets calculate 3A + 4B.

3A is:

Add 4B:

To add 40, move horizontally to the next finger.

B is two fingers plus three vertical jumps. As you jump back to the first finger, your thumb on the right move one digit up.

Result: 3A + 4B = 85. Now, let’s practice subtraction. For example, let’s calculate F1 – 76.

F1:

To subtract 70, just move horizontally two fingers left (which subtracts 80) than go one digit back.

As 6 = 4 + 2, to subtract 6, make one horizontal and two vertical jumps.

Result: F1 — 76 = 7B.

If you want to count numbers larger than 255, grab your younger sister, quickly teach her counting in hex on fingers, and you can easily calculate between 0 and 65535 (0000 — FFFF).

This is how we did ABCD + 1234:

You can add the least significant digit first, or the most significant first, it really doesn’t matter. Just do it accurately.

ABCD + 1234 = BE01

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