I've got that drawing of your somewhere but I can't locate it. Could you
please send me a copy?
thanks
John
----- Original Message -----
From: "tony moss" <[EMAIL PROTECTED]>
Cc: "Sundial List" <sundial@rrz.uni-koeln.de>
Sent: Monday, November 29, 2004 9:46 AM
Subject: Re: Wall Declination Measurement
John Carmichael wrote:
Subject: Wall Declination Measurement
Hopefully, somebody from the sundial list will help us.
This is my own preferred method of determining wall declination but,
before originally adopting it, I needed to be sure that
a) the 'nail' was truly pependicular to the measuring board and
b) the plumbline/pencil line ran exactly through the axis of the nail.
Without this certainty the results might be questionable so to that end I
developed my 'precision declinometer' which I know has been adopted in
various forms by other diallists. It uses a tapered 'gnomon' spike
sliding in a machined vee groove*. The novel idea was to include a
needle point in the butt end of the spike which punctures the recording
paper exactly on its axis.
For anyone who missed the previous offer via this list some years ago I
can supply a gif and jpeg showing how it is made and used.
Like John Davis I also prefer to take a number of readings over an
extended period then take an average.
* An accurately drill hole is almost as good but 'drilling is the least
precise process in engineering' and unless a good sliding fit is obtained
then the tip and needle point can wobble off centre whereas a vee groove
constrains the spike precisely in two perpendicular planes.
Tony Moss
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