On 8/31/12, George Hart <george@georgehart.com> wrote:
Geometrically, both cylinders would be completely smooth at their interface surface. I do not want to have to screw the scales along each other. It would take forever to move from one end of a long helix to the other. Free movement of the two scales is desirable "across the threads" so it is quick and easy to line up any desired values on the C and D scales.
Oh, of course. Two concentric hollow cylinders, the outer one transparent, and with smooth surfaces that just barely allow movement (for proper registration, keeping them coaxial). That's a much better design. It also allows for many more scales, so you could have S, T, L, LL, etc. scales for a full range of engineering calculations. -- Robert Munafo -- mrob.com Follow me at: gplus.to/mrob - fb.com/mrob27 - twitter.com/mrob_27 - mrob27.wordpress.com - youtube.com/user/mrob143 - rilybot.blogspot.com