Hello dialists:
I have been giving more thought to the practical aspects of designing and
constructing a very large sundial, particularly the problem of accurately
laying out the time lines.
THE PROBLEM: The plotting techniques which use tabulated angles or
computation produce timeline plotting angles in degrees which the dialist
must mark onto the dial plate using a protractor. These angles will be as
precise as the number of decimal places used in the calculations. However,
even though one takes great care to obtain precise timeline angles, this
amount of precision is useless if one's protractor isn't equally precise.
The graphical plotting method also requires an accurate protractor, of course.
SOLUTION A: By definition, large protractors are more precise than small
ones. So physically laying out the hour lines for a giant sundial would
require a giant protractor. Even Robert Terwilliger's laser trigon wouldn't
help because it's degree markings are too small. Computer drawn lines don't
help either, because you can't easily enlarge a small paper drawing by a
hundred fold. I'm thinking that during the construction phase of a very
large sundial, I could make a temporary giant protractor located just
outside the hourline radius. This would be a fairly simple thing to do using
plane geometry.
SOLUTION B: If the unit square method is used (Waugh, pg. 40-43), then no
protractor is needed. One only needs a good long measuring tape for laying
out the lines. ( The limits of precision would again depend on the number of
decimal places used.)
SOLUTION C: What if I built the gnomon first and use its shadow to tell me
the position of the time lines???? With this method, no calculations,
plotting, protractors or tape measures are needed. Using a shadow
sharpener, the exact position of each timeline could be marked onto the dial
face. Of course, using this method would require the proper EOT, DST, and
longitude corrections. This method would also work well on an irregular
surface. (I think) Marking the time lines would be easier and faster on
those days when EOT=0, right?
Do any of you have any thoughts on this problem and which would be the best
solution?
Thanks,
John Carmichael
