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What is a vernier scale?

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A complicated maths formula (and a man covering his eyes!); vernier scale, Pierre Vernier, bevel protractor Named after the mathematician who invented it, Frenchman Pierre Vernier (not pictured), the vernier scale is a scale used to determine more accurate measurements (be they distances or angles).
Top; Primary Scale; Bottom; Vernier scale It determines measurements in between those marked on “primary scales”.
The vernier scale (bottom); bevel protractor For angles, the “primary scale” is in degrees, whilst the vernier scale measures in “minutes”.
Wonkee Donkee says "But these minutes are useless for telling the time." 
A one degree angle inside a circle; degrees and minutes, bevel protractor One minute is equal to 1/60th of a single degree.