Hi all,
I have a question/challenge to all you sundial designers: what is the most
accurate design for a Standard Time dial?
The reason behind the question is to find a way to stop members of the
public looking at a public dial, inspecting their watches, and concluding
that dials never tell the right time!
The criteria for the dial are, in my opinion:
a) it should tell Standard Time, (or possibly Daylight Saving Time - BST in
the UK)
b) it should be in a fixed location
c) it must have no moving parts (which rules out adjustable equatorials and
changeable gnomons etc) and
should be as physically robust as possible.
d) it must not require reference to a separate table or computer program eg
to get an exact declination for the sun.
All data must be built into the dial plate.
e) the "accuracy" should be interpreted as the mean error for the hour
lines 3 hours either side of noon (or 12:00) for the years 2000 to 2050.
As a starter, the "Singleton" dial recently discussed here would seem to be
a reasonable candidate. It's main limitation, common to all dials which
incorporate an EoT correction, is that it is drawn for a some MEAN EoT
curve, and no allowance is made for the leap year cycle and the other minor
variations. Is there some geometry of dial plate and style which minimises
the time error caused by small year-to-year variations in the mean daily
declination? If this is achieved, then the small change in the EoT over a
single day may be allowed for.
There is no prize for the competition, but I promise I will build a physical
example of the best suggestion, and share it with the list!
Happy designing,
John
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Dr J R Davis
Flowton, UK
52.08N, 1.043E
email: [EMAIL PROTECTED]
