Re: [ATM] RE: [atm_free] The zonal Foucault test isfreeofinherentcorrection bias - some supporting graphs

[Guy Brandenburg <gfbrandenburg@yahoo.com>]

FWIW, this is also how I have ended up doing it as
well. As it happens, the floor where I generally test
mirrors vibrates because the building's HVAC unit is
nearby; I make it so that one zone is vibrating in and
out of brightness, and then twirl the longitudinal
dial until I get a result that the two sizes of my
target zone are vibrating in and out of brighness at
the same time. 
Guy
--- Bob May <bobmay@nethere.com> wrote:
> Read the last paragraph of Linfoot's treatise and
> you will note one little
> comment on reading the zones where he says that you
> want to be looking at
> the zones as the knife cuts the beam for which side
> darkens first.  It seems
> that a lot of people think that reading the zone by
> strict comparing of the
> two shades of gray as a static display as the camera
> will show is the way to
> do it but I think that watching the two zones as
> they darken as Linfoot says
> is the more proper way to do the test.
> With the static setting of the KE, you are comparing
> two brightness levels
> which may or may not be exactly right.  Watching the
> shadow flicker across
> the two zones is something that the eye can spot a
> lot easier as which one
> starts and finishes first.  I can get to within
> maybe .003" by comparing the
> two zones by a static display but get a lot closer
> when looking at how the
> two zones flicker dark and light when the KE is
> moving.  I suspect that
> James is doing it this way to get the half thou
> readings that he is
> claiming.
> Bob May
> bobmay@nethere.com
> http://nav.to/bobmay
> http://bobmay.astronomy.net
> 
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> ATM mailing list http://www.atmlist.net/
> 

Guy  Brandenburg
Washington, DC
My home page:
http://home.earthlink.net/~gfbranden/GFB_Home_Page.html
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