Tachometer, Magnetic, Waltham, 200-3,000 RPM ca 1930's

Here is a 1930's-vintage magnetic aircraft tachometer, made by Waltham Watch Company. This tach measured engine speed from 200-3,000 RPMs.  The last aircraft which had this installed had a maximum operating limit of 2,300 RPM, as seen by the red line painted on the glass surface. The magnetic tachometer was connected to the engine via cable shaft, and translated shaft rotation via magnetic mechanism and rotated the pointer to indicate the RPMs.   

This tachometer is in exceptional condition for its age.  The convex glass is clear and intact. The dial lettering is precise and distinct.  Measures 3.25 inches diameter by ~3 inches deep.