The method I use to get the declination was suggested to me by Dave Bell some time ago. I have designed a sheet with instructions that I e-mail to the client. He puts the sheet in the spot he wants the sundial to occupy, makes sure the sheet is level, hangs a plumb line and puts a dot at each end of the resultant shadowline at any precise time. He sends the form back with his order and then I reduce the data using the Dialist's Companion and a good protractor. I like it because it can be done at any precise time, not just at local noon.
The accuracy issue that Patrick mentioned is a good point...thankfully my dial is not mounted so a slight rotation can easily compensate for any small errors. The accuracy that I have been able to achieve using Dave's method is close enough for what I am trying to do, and I have been surprised at how close I was able to get each time I tried it here. Actually, I was able to see how out of square one of my walls of my house was!!!
Regards,
Jim Tallman
Artisan Industrials
Patrick Powers wrote:
Message text written by INTERNET:[email protected]>I could envision a packaged "device" you could mail to the customer, wiht
instructions. It would be placed against the outside of the window (or
wall) in question, when the sun falls fully upon it. You would have a
plane surface with a straight edge held against the window, a pin,
perpendicular to the plane, near its far edge, a circular bubble level,
and an inexpensive LCD digital watch. Held on a bar of some sort above the
surface would be a disposable 35mm camera. The user places it against the
window, adjusts until the bubble is centered, and trips the shutter. You
receive the whole package, folded back up, and process the film. The pin's
shadow is seen on a grid printed on the surface, along with the date and
time (set, say, for GMT) of the measurement. With this, you would also
need a protractor arm of some sort, also in the camera's field of view,
that is unfolded to lay flush against the window, at the same time.An alternate form might be to have the "protractor arm" perpendicular to
the plane, also, and a linear bubble level, exactly parallel to the
"back" edge, for levelling on one axis only. The user takes TWO pictures,
some days apart, and again, you do the math from the shadow images.<If only one could rely on that! Sadly the variation between successive
measurements even over say an hour - and even with one of Tony Moss's
excellent declination measurement devices - is such that one has always to
make some average estimate and possibly eliminate from that avearage the
highest and lowest individual measurements. If the dial is to be at all
accurate (and fortunately most vertical dials are not delineated in less
than quarter hours!) my experience is that it is very difficult to be
confident about the declination of a wall to within +/- half a degree. Can
anyone confidently and consistently do better?Patrick
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