Further to Roy Anthony's note on laying out a large dial.
His method is similar to the one used for the Swenson dial which is 30 by
60 feet. An arm with a scale attached was pivioted at the base of the
gnomon. This was the origin of the original x-y set of points defining the
dial lines. Another scale was layed horizontaly along the top of the wall.
A seconded arm with attached scale was pivioted at a set of predetermined
points along the horizontal scale. Each x-y point was converted to a pair
of readings on the pivoted arms. A spread sheet is excellent for this. A
drill was placed through a hole on plates attached to each arm. This
located the point to about 1/16 of an inch. This is much less than the
reading accuracy of the shadow (about 0.5 inch) due to the penumbral
effects.
Hope this helps.
Cheers,
John
Professor John P.G.Shepherd
Physics Department
University of Wisconsin-River Falls
410 S. 3rd. St.
River Falls,WI 54022
Phone (715)-425-3196, eve. (715)-425-6203
Fax (715)-425-0652
