We sometimes see the letters "MN" on the movements of Heuer chronographs and dashboard timers, perhaps limited to the movements made by Valjoux. These letters usually are marked under the balance wheel, or on the plate under the balance wheel.

I have always assumed that this is the code that allows the movement maker (say, Valjoux) to indicate which brand the movement was produced for.

Does anyone know of a reference / table that indicates the codes that were used for the various brands? Any other information on this point?

Thanks,

Jeff