Speedometer code

[Oliver Pi]

Hello All,
Can anyone offer facts, figures or reference material explaining the cryptic numbers and letters found on the Smiths speedometers and speedometer drive units? 
Farewell for now,
Oliver

[JulianS]

The numbers on the speedometers relate to the internals and application of the device.

The numbers on the gearbox relate to ratio, direction of rotation and spindle diameter.

There are literally dozens of numbers, more for the chronometrics than the magnetic instruments.

Smiths issues catalogues, annually in the late 1950s and the 1960s and into the 1970s detailing the applications.

Are you looking for information on any numbers in particular?

[Oliver Pi]

The bike I am working with had no speedometer or drive unit when I purchased it.  The parts manual (1970 BSA Starfire) calls for a BG.5330/31 drive unit and the speedometer head designation is given as SSM.5007/02 for miles per hour.