The Compass Sundial

Ingenious Combination of two Sundials

Cut-out sheet for a double sundial following a design from the 19th century.

This special type of sundial was invented by the Greek astronomer Ptolemy (AD 100-160) and rediscovered in the 19th century by French clockmakers. They combined an analemnic sundial (featuring a date scale that accounts for the changing solar declination during a year) with a simple horizontal one. The vertical shadow thrower, or gnomon, is set to the correct date and the instrument is turned until both sundials show the same time. Now the sundial is facing exactly north, without the need of a compass. In the past this kind of sundial was produced for only for a given latitude. Further north or south they became more and more inaccurate. But that does not apply to the AstroMedia Compass Sundial: 

Our sundial can be adjusted to all latitudes between 26° and 65°. The dial shows the time following two different methods, which enables you to find true north. You can read apparent local time (solar time) as well as "normal" time.

The Compass Sundial doesn't need a compass to orient it and can be adjusted to all latitudes between Oslo and Cairo.