Rotary indicating instrument with magnetic reset

A crystal unit for the viewing end of an indicating instrument having a rotatable indicating hand adapted as it rotates to advance a maximum hand, the unit comprising a transparent crystal having a solid body, the body having a first stub shaft fixed thereto and projecting axially from an inner face thereof, and a second stub shaft fixed thereto and projecting axially from an outer face thereof;

• a friction washer disposed on the first stub shaft adjacent the said inner face, a maximum hand slidably and relatively rotatably disposed upon the first stub shaft rearwardly of the washer, an inner magnet slidably and relatively rotatably disposed upon the first stub shaft between the washer and the maximum hand, the maximum hand having a hub portion of magnetically attractible material, and retainer means on a free end of the first stub shaft blocking endwise escape of the washer, magnet, and maximum hand;
• an outer magnet in the form of a knob slidably and relatively rotatably disposed upon the second stub shaft, and retainer means on a free end of the second stub shaft blocking endwise escape of the outer magnet, the hub of the maximum hand being attracted to the inner magnet, the inner and outer magnets being magnetically attracted toward each other, and the washer being pressured against the inner face of the crystal by the attraction of the inner magnet to the outer magnet so as to frictionally engage the washer with both the crystal and the first magnet.

An indicating instrument including a casing having an open front end, a scaled dial fitted in the casing proximate its open front end, a rotatable drive shaft extending axially through the casing carrying an indicating hand on an end thereof forwardly of the dial, a transparent crystal having a solid body closing over the open front end, means sealing the crystal about its outer edging relative to the open end of the casing, the crystal having an axially extending integral inner stub shaft and an axially extending integral outer stub shaft, a magnetically attractible maximum hand slidably mounted upon the inner stub shaft for relative rotation, a first magnet slidably and rotatably disposed upon the inner stub shaft toward the crystal side of the maximum hand magnetically attracting the latter hand to it, a friction washer disposed upon the inner stub shaft between the first magnet and the crystal, a second magnet mounted externally of the crystal upon the outer stub shaft for relative rotation, the first and second magnets being magnetically attracted toward each other whereby the washer is caused to exert a predetermined friction force on both the crystal and the first magnet so as to effect upon the maximum hand a predetermined drag resistance to relative rotation of the latter, the indicating hand having a forwardly extending ear adapted under torque of the drive shaft as the indicating hand is rotated by the latter in one direction to engage the maximum hand and angularly advance the latter ahead of the indicating hand against the said drag resistance, and the second magnet being manually rotatable in a reverse direction so as to overcome the friction force of the washer and carry the first magnet and the maximum hand with it in said reverse direction.