SUNDIAL

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The other dimension needed to lay out your sundial can be calculated by first drawing a semicircle using Dimension A as the diameter (see Fig. 1). Construct a tangent perpendicular to the diameter of the half circle, and then scribe a line that diverges from the intersection of the diameter and the tangent at an angle equal to your latitude. The length of the chord which is described by that line's intersections with the semicircle will become Dimension B.

You can now begin to draw the dial face on a piece of tracing paper. Prepare a threesided figure like the one depicted by the solid red lines-and according to the dimensions specified—in Fig. 2. The dashed red lines in the same illustration indicate the noon and six o'clock lines, which intersect each other at a 90° angle at the focus (or center) of the dial. Extend the two broken lines perpendicularly from the solid red lines to points that are a distance equal to Dimension A beyond the three-sided figure on the six o'clock line, and a distance equal to Dimension B below it on the noon line . . . as shown.

CHART A 
TIME ZONE MERIDIANS

Eastern Standard Time = 75° West
Central Standard Time = 90° West
Mountain Standard Time = 105° West
Pacific Standard Time = 120° West

Each of the three points thus arrived at will now serve as a focus from which the hour line determinants (Fig. 2 shows them in blue) will radiate at 15° intervals. But before you can put those reference lines on paper, it's necessary to figure out the correction factor for your longitude's difference from your time zone's meridian.

Consult Chart A to learn whether you're situated to the east or to the west of your time zone's meridian. In either case, subtract the smaller number from the larger one. If your location's longitude happens to be west of the time zone longitude, correct for the difference by rotating the six o'clock and noon lines clockwise—from their three respective focuses-that number of degrees. But if your home is located to the east of your time zone's meridian, correct by rotating the six o'clock and noon line determinants counterclockwise. (A clockwisewest of meridian-correction is shown by the blue lines in Fig. 2.)

With that done, you can proceed to place the hour line determinants on the paper by marking off a 15° increment for each hour, as shown, and then connecting the focus of the dial to the points where the determinants intersect the solid red lines. These connecting lines, shown in green in Fig. 2, will become the hour lines on the sundial's face. Complete the dial by scribing its perimeter (with a diameter equaling Dimension A) and lettering the Roman numerals.

MAKING THE DIAL

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