Sundials are divided into two main groups:
- Altitude dials determine the time from the sun's altitude
(the sun's height above the horizon). These dials either have to be
correctly oriented to the compass directions or they have to be aligned
to the sun.
- Azimuth dials determine the time from the hour angle of the
sun (the sun's angle on its daily arc). These dials have to be correctly
oriented and therefore a magnetic compass is often incorporated in the