Sundials tell accurate time during daylight hours. The first sundials were used more than 3,500 years ago in Egypt.

Why do stores sell sundials that are not accurate?

• It’s inexpensive to mass-produce identical sundials with no concern if the sundial displays accurate clock time.
• The seller and buyer may not know enough about sundials and how to cureate sundials that display accurate clock time.
• Some buyers are looking just for a lawn ornament and have no desire to properly set up their sundial.

Accurate Sundials

What makes an accurate sundial design?

• The angle on the gnomon must be parallel to the earth’s axis and does not require adjusting for the changing height of the sun during the changing seasons. This angle must be equal to your latitude to display accurate clock time.
• The position of the hour lines must be calculated and laid out based on your latitude. Generally, the farther south the sundial, the closer together the hours near noon and farther apart at hours nearing sunrise and sunset. The hour lines will not be equally spaced.
• Same longitude, different latitudes notice the difference in the height of the gnomons – laying on their sides – and the positions of the hour lines.
• The position of the hour lines must be calculated and laid out based upon your longitude. There can be a difference of almost 2 hours, in some time zones, between two identical sundials, one placed at either East-West end of the time zone.