Callibrating a Veigel Tachometer

[spider rust]

Does anyone know the no. of cable turns that a solo or sidecar crown wheel and pinion would give over a set distance?
Say 20 meters.
My reason for asking is to try to work out what the gearing is in my Veigel Tachometer, as the dial plate is a marriage to the case.
In other words the dial plate is an original for the side car 120kmh. But the case gearing its fitted to might be solo?
Confused? I am!

[schrader7032]

Tachometer or speedometer?

If speedometer, I noticed something that might be interesting. Normally, the speedometer has a small number on the face, like W=1.112. This number means that the cable turns 1112 times in one mile of distance. Scaling down by 100, the cable would turn 11.12 times in 52.95 inches. One could experience that by putting chalk marks on the ground at this distance, a paper clip on the exposed cable, and then pushing the bike exactly that distance.

I did some match where I divided the rear drive ratio (say 33/11) by the W number on the dial. For /5-on bikes, that ratio is essentially 2.70. For pre 1970 bikes, that ratio is close to 2.60. It looks like if the transmission is a sidecar variety, that number is about 2.48.

So, knowing the rear drive ratio, one could count the roll the bike and count the number of turns which might lead to a specific speedometer requirement.

If your question is about a tachometer, then never mind!!