Re: [ATM] Was Aluminum Mirror, now Spherometer

["Bob May" <rmay@nethere.com>]

Actually,,  the equations needed are very simple ones.  In
addition, the measuring tools don't need to be all that precise
for our needds.  Go look on my site for the spherometer formulas
and see how much they vary for an error of meauring of five
thousandths of an inch.  In addition, the center can be off by a
fair bit and still measure right for our needs.
I'll also note that the bigger the spherometer, the more accurate
it is for any particular depth measuring tool.  I usually use
half or quarter thousandth of an inch dial indicators and get a
good agreement with theactual ROC of a polished mirror.  Please
note that on ground mirror surfaces, the balls can fall into a
pit hole and thus be off by a little bit.
Bob May
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