How to Use a Sundial Clock

The sundial is an ancient device used for measuring time. The earliest known sundial clock dates back to 1500 B.C., constructed in Egypt under the reign of Tuthmosis III. The book "Sundials" reports, however, that other solar clock and calendar devices probably existed long before these known Egyptian examples. A sundial does not measure hourly time as precisely as a digital watch, but if you know how to use a sundial properly, the hourly estimates are fairly accurate.

Compass

Instructions

- 1
  Locate north using a compass, or use the sun's position to estimate due north. The sun rises roughly in the east and sets in the west. Sunrise and sunset are not due east or west, so a compass provides more accurate results.
- 2
  Position the sundial so its spire points north. For a permanent sundial installation, you can assume it is calibrated to face north, but a small sundial in your back yard may need adjustment.
- 3
  Count the number of hour lines from the center position to the sundial's shadow. Think of the spire's shadow as the hour hand on a normal clock.
- 4
  Subtract the hour lines from noon if the shadow is to the left, or add the hour lines if it lies to the right. For example, three hour markers right from center would be 3:00 p.m., or 15:00 in military time. Smaller marks in between hourly markers indicate equal increments. For example, a sundial with four even spaces between each hour provides incremental measures of 15 minutes each.

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