Gauge

This is the British and Canadian spelling while in the United States it is sometimes spelled without the "u" (gage). It is becoming standard to use "gage" for wire size and "gauge" for an instrument.
[1] An instrument that registers the quantity of a substance, e.g., ammeter, boost gauge, fuel gauge, gas gauge, in-dash gauge, oil gauge, oil level gauge, oil pressure gauge, oil temperature gauge, outside temperature gauge, temperature gauge, tire gauge, tire pressure gauge, turbo gauge, vacuum gauge, voltmeter, and water temperature gauge.
[2] A tool for measuring clearances, pressures, sizes, etc.
See also adjusting gauge, B & S gauge, brake gauge, caliper gauge, compression gauge, compression tester, depth gauge, dial gauge, disc brake gauge, feeler gauge, frame gauge, ignition gauge, screw pitch gauge, sighting point gauge, spark plug gauge, thread gauge, thread pitch gauge, throttle gauge, tire tread gauge, tram gauge, tread depth gauge, vernier gauge, wheel alignment gauge
[3] A measurement of tubing. See plain gauge tubing