Re: Marking Technique

[William S. Maddux]

Hello John, Firstly, congratulations on accomplishing so much. Nothing would please me more than to learn that my concerns are unfounded.   >If we did our marking correctly, the biggest factor affecting precision will >be the straightness of the styles. I suppose this could be checked exactly >by using a laser, but lacking one, all we could use was our eyes. By placing >one eye at the base of a style, we could look straight up the edge of the >styles. We did see very slight undulations in the styles, but we >guesstimated that they were only between I and 3 inches, a very small amount >if you consider the enormous size of the sundial. These could only affect >the precision of the dial by a few seconds. Time will tell!   I've taken a look at the first drawing (right after the photos) in the proposal. It is an elevation view from the west, that has a superposed set of lines that show about the largest layout possible using the side edges as styles. Looking at the labeled distances along the "ground level" northward from where the west edge meets ground level, a red line inclined at about 58.04° shows the intersection of an equinoctial plane with the (meridian) plane of the drawing, and two lines north and south show limits at the respective solstices, making angles of 23.4° with the equatorial line. All three lines converge to a point on the ground about 8.84 meters north of the southern limit of the base of the heliostat tower. The length along the ground from the origin of the west edge/style at the south to the convergence point of the three red lines at the north, scales out to about 51.22 meters. The distance within the equatorial plane from the convergence point to the style is calculable as about 27.1 meters. This line of course meets the style perpendicularly. At that distance, an arc of 0.25°, if rotated about this equatorial line, would trace out a circle of about 9.3 inches diameter.  Thus at that distance, the time required for the 1/2° degree wide sun to pass through the meridian plane would be very nearly 2 minutes of time during which it would move about 9.3 inches relative to the style edge. Therefore, if the style's edge were to be laterally displaced 3 inches, the resulting error in time would be about 3/9.3 x 120 = 38.7 seconds of time, and a 1 inch wrong location of the effective edge would cause nearly 13 seconds of error.  Bill