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Serle's Dialing Scales

Dialing scales are geometric aids–nomograms–that drastically simplify the task of laying out sundial hour lines. Serle's scales can be used to design a wide variety of planar dials, including horizontal, vertical, polar, inclining, and declining.

The markings on such rulers allow the complex mathematics of dial construction to be bypassed.

In addition to dial construction, these scales can also be used to reverse-engineer a dial, using only the hour lines to reveal the latitude for which it was designed.

British Sundial Society

How to use
(Drawing a horizontal dial)

1. Draw two perpendicular lines.

2. Lay the ruler along the horizontal line, positioning the beginning of its latitude scale at the intersection of the two lines.

3. Consulting the latitude scale, make a mark along the horizontal line that corresponds with the appropriate latitude. If the dial is horizontal, use the latitude of use. If vertical, use the colatitude (90º-latitude).

4. Place the 6th hour mark on the marked point on the horizontal line and the 12th hour mark on the vertical line.

5. Consulting the hour scale on the ruler, mark each hour point. Next, connect each of these points to the origin.


6. For the hours before 6am and after 6pm, extend the opposite hour lines downward through the origin.

Constructing a Horizontal Dial
Reverse-Engineering a Dial's Latitude
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