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?
I would suspect that for the same reasons that it is hard to measure declination to better than +/- half a degree, that there is not much point in doing so. Walls are not always straight and they are not always flat. What if you accurately measure the declination of a window in a wall and then mount a sundial on some irregular clapboards that have a declination different by one degree? I think the better solution is a method of mounting that allows adjustments on the order of +/- 1 degree. The adjustments can be made during/after installation based on observations of the shadows at various times. As my father often said, "What in the heck would the carpenter do, if it weren't for the painter with putty and glue."
--Art Carlson
