How to find zero? - the clock face is rotary
A highly precise sensor which adjusts electric ignition.
The sensor determines the position of piston and thanks to it adjusting the ignition can be very precise.
The thread: 14x1,25 mm
Adapter is made from steel in "golden" zinc coat.
This
device is very useful In adjusting ignitions of a variety of engines
(Triumph, Norton, Harley-Davidson, Indian, Simson, NSU, DKW, BMW, AJS, BSA, Zundapp, MZ, Honda, Suzuki, Yamaha, Kawasaki etc.)
The sensor is brand new, in good working order. It has been never used before.