Shaft 1, on which tapered friction disk 2 is keyed, is driven by the shaft whose speed is to be measured. Tapered disk 5 is pressed against disk 2 by spring 3 of governor 4. This drives the governor. When the governor reaches a definite speed, the centrifugal force of balls 6 overcomes the resistance of spring 3, withdrawing wheel 5 from wheel 2. Thus the speed of the governor shaft never exceeds a certain constant speed, regardless of the speed of the shaft being tested. Bevel gear 7 meshes with bevel gears 8 between which roller 9, keyed to shaft 10, is located. The two gears 8 are pressed against roller 9 by spring 11 and drive it at a speed which corresponds to the distance from the plane of the roller to the axis of rotation of the gears. Worm 12 meshes with worm wheel 15 which is driven from shaft 1 through worm 13 and worm wheel 14. The hands of worms 12 and 13 are such that when the tachometer is switched on, worm wheel 15 tends to shift shaft 10 downward, and roller 9 tends to shift it upward by screwing worm 12 "out" of worm wheel 15. The whole system and hand 16 come to equilibrium when roller 9 is at the position with respect to the axis of gears 8 in which the velocity of the raising of shaft 10 from the rotation of roller 9 equals the velocity of the lowering of the shaft from the rotation of worm wheel 15 The higher the speed of the shaft being tested, the lower roller 9 should be with respect to the axis of gears 8 to achieve equality of the two motions of shaft 10 and, consequently, the greater the angle through which speed indicator hand 16 turns in the counterclockwise direction.
$3444$CF,M$