Hello everyone,
I'm planning to make a small vertical west dial, about 1m for the width
of the dial face, at my latitude of 49N. It will not use a nodus.
The angular width of the sun makes it hard to get a really accurate time
reading, but there will also be small errors from mis-positioning of the
dial plate when installing (declination and inclination), imprecise
positioning of the gnomon or the hour lines, and perhaps other causes too.
First, questions directed at those of you who have practical experience
of creating vertical sundials: If I'm careful and have a well-machined
gnomon, what level of accuracy might be achievable in practice? I assume
+/- 5 minutes throughout the day and year is fairly easy to achieve, but
what about +/- 2 minutes, or even +/- 1 minute? How well did you do? How
did you measure your wall's declination?
Second, have there been any studies of how well dial users compensate
for a penumbra - by which I mean gathering data from volunteers,
studying the spread of errors in time readings taken from a dial versus
a reference time source? (without employing a shadow sharpener)
Thanks,
Steve
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