Tachometer cable rpm

[aldo]

Can some one tell me the rpm of the tachometer cable relative to engine on my 1959 Dexta? Does the cable spin at the same rpm as the engine or a ratio? I'm toying with the idea of making a simple output for electronic tachometer.

[Old Hywel]

Cable turns at half engine revs. There’s usually ‘2:1’ on the clock face.

[aldo]

Thanks.