Thanks for the information about the circumstances of the dial's
time-reading.
One more thing I should mention:
To azimuth-align the dial by adjusting it to say the time that it should
say, it isn't necessary to interpolate the dial's time-reading. You could
ask the relevant people at what approximate clock-times they'd like to
consider azimuth-aligning the dial. Then you could calculate as follows:
1. Calculate what local true solar times correspond to those times that
they mentioned.
2, Determine and choose what whole (integer) hour true solar times (or
half-hour times, if the dial shows them and one of them is closer) are
closest to those local true solar times that you calculated in paragraph #1
above.
3. Then calculate what clock-times correspond to those times chosen in
paragraph #2 above.
On a notebook-page, write down, on separate lines, each of the clock-times
in paragraph #3 above, and next to it, on the same line, the local true
solar times chosen in paragraph #2 above.
Advise the relevant people to choose one of those listed clock-times, and,
at that time, rotate the dial so that it shows the whole or half-hour local
true solar time that is written next to it on the same line.
And it goes without saying that any dial-time and clock-time comparisons
made for the purpose of calculating the azimuth-alignment error should be
done at times when the dial-time is such that the shadow is exactly on an
hour-line, half-hour line, quarter-hour line, 10-minute-line...or, in other
words, some line on the dial-fact. In other words, you can and should
choose a clock-time for the comparison, at which you aren't going to have
to interpolate the dial-time.
-
One more thing:
If two different clock-time/dial-time comparisons give different values for
the azimuth-alignment error, then that suggests that the dial has more
problems than just its azimuth-alignment.
>From various points on the north and south edges of the equatorial band,
measure the distance from the edge of the band to the center of the
band-circle. ...to find out if the equatorial-band is circular and the
gnomon is centered in it.
Look at the dial from the side, using a T-square, to judge whether the
gnomon is perpendicular to the edges of the equatorial-band.
I'd expect that, if it's off enough to cause a 22.5 minute problem, the
non-perpendicularity would be quite noticeable.
Inexpensive Band-Equatorials, such as inexpensive Armillaries,always do
terribly by these construction-standards. Out of round band, uncentered,
non-perpendicular gnomon.
Michael Ossipoff
...
On Tue, Sep 25, 2018 at 9:26 PM Steve Lelievre <
steve.lelievre.can...@gmail.com> wrote:
> Yep, that's it.
>
> Steve
>
> On 2018-09-25 6:09 PM, Hank de Wit wrote:
> > Is this the dial?
> >
> >
> https://s3.amazonaws.com/gs-waymarking-images/4ac8dd87-b79b-42a0-9a14-08e86890c14d.JPG
> >
> https://c8.alamy.com/comp/AWRMGN/sun-dial-van-dusen-gardens-vancouver-bc-canada-AWRMGN.jpg
> >
>
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>
>
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