Digit comes from fingers—and base decides how many you need
A digit is one symbol in positional notation, like 0–9 in everyday base ten. Latin digiti meant fingers. Binary needs only 0 and 1; hexadecimal borrows letters up to F because sixteen values will not fit on ten fingertips.
For integer bases, the count of distinct digits equals the absolute value of the base, each digit standing for a whole number from zero up to one below the base. Each position carries a place value, and a numeral's total is the sum of every digit times its place weight. In 10.34, the 1 means one ten, the 3 three tenths and the 4 four hundredths, while the 0 adds nothing but keeps the 1 in the tens column. English marks the units place with a point, much of Europe with a comma.
Other traditions used digits too. Maya numerals, possibly older than the Hindu–Arabic kind, counted in twenties with a shell for zero, stacked vertically with units at the bottom and no way to write fractions. Chinese and Japanese rod numerals, written forms of counting rods, formed a decimal positional system that could show zero and even negative numbers. Thai digits work exactly like Hindu–Arabic ones with different shapes.
Computing leans on binary, octal and hexadecimal, and the base-3 variant called balanced ternary, with digits 1, 0 and −1, ran the experimental Russian Setun computers. Augustin-Louis Cauchy argued for signed digits in 1840. Digits matter little to modern mathematics, but some ideas depend on them: digital roots, the hand-checking trick of casting out nines, repunits like 1111, and the open question of Lychrel numbers, whose smallest base-10 candidate is 196.
Counting began on bodies; some cultures used knuckles, finger gaps and toes, and the Oksapmin of New Guinea map numbers onto 27 points of the upper body. Sumerians stored quantities in clay tokens between 8000 and 3500 BC before pressing number signs into tablets.
Source: Numerical digit
