Very interesting.
The ad suggests that it is not a shaft-driven tachometer, per se, in that it appears to rotate with the record it is sitting on while the arm is down on the record.
It must work on some sort of spring or weight and lever system which translates the centrifugal force generated by rotation into an RPM measurement.
I would assume that it is used with a record and the tone arm so that the rotation speed is calculated with the drag of the record and needle, although I don't see how this would work with the tone arm illustrated--great potential for disaster in this picture.
The ad doesn't say whether it has a scale for a range of speeds or whether it is just 78 RPM.
Does anyone own one? How does it work?
It is a cool looking device, but I would think a cheap digital laser tachometer would be more practical now.
