Shaft A of the tachometer is driven by the shaft whose speed is to be measured through shaft D and gears 1 and 2. Lever 4 with weights 5 is pivoted on link 3 which is keyed on shaft A. When shaft A rotates, the moment of the centrifugal forces acting on weights 5 tends to turn lever 4 so that connecting rod 6 displaces sleeve 7, turning crank lever 8 and hand 9. Hand 9 indicates the angular velocity of the shaft being tested. Spring 10 returns lever 4 with weights 5 to the initial position.
$2530$LrG,M$