Shaft A of the tachometer is driven by the shaft whose speed is being measured through speed gearbox 1 which enables the range of speeds that can be measured to be extended. When shaft A rotates, the moment of the centrifugal force tends to turn annular mass 2 to the vertical position, overcoming the resistance of spring 3. This motion is transmitted to hand 4 by connecting rod 5, sleeve 6, lever 7, which is rigidly attached to segment gear 8, and pinion 9. Thus, the angular velocity of the shaft being tested is indicated on scale 10.
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