O/K, now I have got it, I think. Silly me,

trust the Germans (or Americans) to get things a#se about face. In the meantime I racked up a quick example (US wheel) in Paint Shop from your picture. Now when I compare the readings between the two I get a 0.4 knt increase in speed on the German one against the US one. Could be my assembly is not quite correct or it could be that the German one is a little faster !! vorsprung durch teknik. :hmm:
Still, many thanks, can now go ahead with speeeeed calculations.