Short for galvanometer; an instrument that detects and measures small electric currents.
Shortened form of 'galvanometer,' which comes from Luigi Galvani (the physicist) combined with -meter (Greek for 'measure'). This colloquial abbreviation appeared in the early 20th century.
A galvo is so sensitive it can detect currents so tiny that thousands of them flowing together wouldn't power a single LED—they're the reason we know lightning creates electromagnetic signals and helped scientists understand how electricity behaves.
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