Re: Drawing circular log scales?
I thought I'd refresh my old Galva skills my trying to replicate the OP's dial based on the photograph shown in Post #12. The first PDF shows a log scale in blue superimposed over the photograph. Clearly there are differences which indicate the original instrument scale is NOT logarithmic, and probably cannot be accurately represented by any mathematical function. So, using the 'measurement' technique suggested by Jean-Paul Gendner in his Galva Help file, by Jeremey <Pamphonica> in Post #23 and by myself in previous designs. the second PDF shows in red a perfect match. If Richard <Mole24UK> is still looking for a true restoration of the original scale, this will provide the art work. I have assumed that the '1' and '10' marks correspond to the full CCW and full CW rotation of the dial, through the measured 285 degrees.
Now, I wonder whether the empirical nature of the original dial may be because the resistance(?) of the control component was only an approximation to logarithmic progression as, I think, is usually the case with most log-law devices.
Mike
|