NavList:

Hello Harri,

Thank you so much! That is fantastic. I had hoped there was a mathematician out there who would take up the challenge, but I never thought it would be done so quickly! Perhaps one day you can explain to this simple non-mathematician  how you do it?

Could I ask you a big favour? If you look at the Luykx paper and the photograph of the actual model at the Smithsonian, you see there are 2 transparent rotors, one with Verniers B and I think Y (not shown, off the diagram)  and the other with Verniers A and X with the scales running in the opposite direction.(the photograph shows side A/X) These rotors are placed on either side of the base plate which has identical copies of the dot scale. The non dot scale you have provided is actually the same as rotor side B in the Luykx paper. In order to build a working replica, I would also need a rotor like side A. I think it is the same, but with the circumference/ellipse  scale going in the opposite direction. Are you able to easily do that? Also, ideally, if it is possible, we would want to add the A and X and B (and Y?) Vernier scales, not shown in the Brown paper. The Vernier index box  on the base plate tells you which side to use depending on rules.

If any of that is possible, I will try printing off the dot scales x2 on paper, stick them to either side of a base plate and print 2 rotors A/X and B/Y on transparency film. As you say, for navigational accuracy, the pivot point would have to be exactly constructed, but I will probably just use a pin for the initial trials. If it works, I will try to build a working model using acrylic sheets and accurately  machined pivot holes like on a circular slide rule.

Thanks again Harri. I’m sure Helsinki is looking beautiful with the snow at 60 N. It is relatively warm, windy and very wet down here in Cornwall at 50N.

Francis