Roger Bailey wrote:
>
> Hello Fellow Dialists,
>
> I was pleased to see the overwhelming response to my posting on determining
> wall declination through the window. Obviously I was not the only one
> frustrated by the usual methods and interested in a simple, one measurement
> technique.
>
> I would like to raise some cautions on accuracy.
>
> 1. Take readings when the sun is low. My initial data involved readings
> when the solar altitude ranged from 0 to 10 degrees. Even if the frame
> casting the shadow was not truly vertical, the error would be small.
> Applying the technique at noon in the tropics would be a different story.
> If in doubt, hang a plumb bob near the glass to get a true vertical. The
> shadow of the plumb line cast over the side of the paper pad held against
> the window would give an accurate relative azimuth.
>
> 2. The paper pad has to be horizontal. If you are lucky, the window sill
> will be satisfactory. Otherwise you are back to the rigging that this
> technique was to avoid.
>
> 3. Remember the declination is the direction the wall faces. This is
> perpendicular to the heading along the wall. Yes a picture is worth 1000
> words but it is harder to send by e-mail.
>
> I would be interested in feedback on your success with the technique. I
> have a series of readings taken in Australia. For the first four
> measurements, taken in the morning, the declination results agreed to
> within half a degree. The afternoon readings were obvious outliers, 3 to 5
> degrees off. I blame the magnified error on the higher solar altitude.
>
> Cheers, Roger Bailey
Roger,
The way I found the declination of my fences and home was to hang around
early in the morning and record the time that the sun just Grazed down
the fence or house. Then using the Dialist companion found the azmuth of
the sun and went from there.
Bob Haselby
San Diego
