Gray code
A binary sequence in which only one bit changes between successive values — so a reading can never get stuck mid-jump between two numbers.
The code takes its name from Frank Gray at Bell Labs, who patented it in 1947 for pulse-code modulation, but the idea is older: Émile Baudot used a variant in his telegraphs back in the 1870s. The trick is that neighbouring values differ by exactly one bit. A rotary encoder coded in straight binary can flash nonsense intermediate values when several tracks flip at once — with this coding that is impossible.
It later turned up in Karnaugh maps, error correction, and position sensors. In the prehistory of computing it belongs among several attempts to make binary machines robust against their own noise.