Article of the month September

Altitude dial 4

Inclined backplane

Here is another example of an altitude measuring sundial. It is quite small, and can be worn as a necklace.
The photographs show the sundial closed, left; and opened for use, right.

The pattern of date and hour lines is on an inclined backplane.
In the front is a small hole that is aimed at the sun.
With the sundial suspended from a string, one lets the light spot fall on the appropriate date line. Then, time may be read.