ATM Foucault Frustration

["Bennett, Thomas D" <thomas.d.bennett@lmco.com>]

Hi ATMs,

When this newbee Foucault tester was trying to test a 10" mirror last night,
I noticed that the COC for each zone systematically changed between each
reading cycle which made it impossible to get decent precision on the
readings. After 3 hours of trying to get consistent readings with no
success, I noticed that the COCs had increased gradually by over 0.25" for
each zone over this period. Could the cycling of the room heater while
trying to maintain a constant room temp have induced thermal waves into the
mirror which would cause these COC changes. If so, what would be a good way
to thermally pre-condition the mirror during the day so that it would be
ready for testing when I return from work in the early evening?

Thanks - Tom