Rotation is transmitted from the shaft whose speed is to be measured through shaft 1 and gear 2 to shaft 3. When shaft 3 rotates, the centrifugal force acting on weights 4 spreads them so that spring 5 is compressed. The displacement of sleeve 6 along shaft 3 turns segment gear 7 and hand 8 which indicates the rotational speed. Sleeve 9 is rigidly clamped on shaft 3. Hair spring 10 eliminates backlash in the links of the mechanism.
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