Sundial layouts, computed & drawn for the cutting machine

Declinometer

A vertical dial is only as good as your knowledge of which way its wall faces. A phone compass is easily ten degrees out next to brick, steel and wiring, and maps rarely do better. The sun can't be wrong. One shadow, one moment and a protractor will give you the wall's direction to within a degree.

  1. Hold or prop a board level against the wall, sticking straight out from it. On the board, draw a line square to the wall (the dashed line).
  2. Stand a pin, nail or pencil upright on that line, or hang a plumb line just above it.
  3. When the sun is on the wall, mark the shadow at a moment you note to the minute, from a clock you trust. Phone clocks are set by the network and are fine.
  4. Measure the angle α between the shadow and the square line with a protractor. Note whether the shadow leans to your left or right as you face the wall.
  5. Enter it here. Take two or three readings half an hour apart; they should agree within a degree.
I.Where
II.When
III.The shadow

Left and right as you stand facing the wall.