[ATM] ATM re: foucault pitfalls

["The Alarm Co." <tac@i1.net>]

The biggest pitfall I encountered was not in building the tester, but
performing the test.  Those jokes about trimming your eyelashes (or corneas)
on the knife edge are more truth than nonsense.  It is necessary to get your
eye very close -- single digit millimeters -- to the KE to see the patterns.
That's one reason video is becoming so popular.  Mount the camera, no more
worries about getting into the right position.

As for building the tester, I used a cheap cross-slide vise from Harbor
Freight.  Clamped the Ke & light in the jaws, stuck a dial indicator with
magnetic base to measure travel.  Boom, done!  I did it that way just
because I could cobble it up in nothing flat from stuff on hand, but it
worked so well I never got around to building a special purpose tester.

 *  Best regards, Bob
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