Re: [ATM] Weird Foucault readings

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

The big question is when you made those older readings, did you let the
mirror cool or did you immediately test it to see where things were?
You can get some real wacky readings if you don't allow cooling.  I got
reminded of that myself today again with a plate glass mirror that I threw
up on the tester and got a center reading.  Over the next 10 minutes, that
center reading changed by .025" or so and was still moving when I stopped
for the day a good 15 minutes later.  The guy, fresh from Chicago a month
ago, came into the class and wanted to finish his Cassaro mirror blank up.
He had a nice sphere with a little hole in the middle and now he's got a 1
wave paraboloid or somewhere in that region at the moment.  The glass was
still moving fast enough that readings changed as time went along.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net


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