6 Mar
2013
6 Mar
'13
10:16 a.m.
> You do NOT need nor want Wikipedia for that!
> Not good to become dependent:-)
> Circumference is PI times diameter.
On Tue, 5 Mar 2013, Jim Stephens wrote:
I should have checked the math. it isn't pi
circumference. It is a
spiral, not a circular scale. I didn't want to try to guess, or
calculate it because I didn't recall how many times it wrapped.
3 * 8 inches isn't the right number either.
Ah! Sorry
I thought that we were still talking about circular.
Flat spiral? (like a [non-computer] "record" (ancient predecessor of
MP3), or like an SA400 stepper cam))
or helix? (like a "wax cylinder" (predecessor of "record") or lead
screw
(such as a Micropolis stepper))
If flat spiral, we can estimate the length by PI times the
arithmetic mean of the diameter (add the innermost, outermost,
and appropriate intermediates and divide by number of turns)
If helix, we can estimate the length by the hypoteneuse of
a right triangle (consisting of the small distance along
the cylinder of the start and end, and the [multiple]
circumference (diameter of the cylinder times number
of turns times PI)) It won't be MUCH different from
just the circumference times nuber of turns.
For the squares and square roots needed for calculating the
hypoteneuse, use the A and D scales (or B and C) of the slide rule.
If the C and D scales do not have a mark for PI, add one.
--
Grumpy Ol' Fred cisin at xenosoft.com