Sundials have been used since ancient times to tell the time of day. They use shadows cast by a gnomon onto a chart of times on the dial. Differences in global positioning need to be accounted for to read the sun dial correctly if you want to know the exact clock time.

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Sundials give a solar time, which needs to be converted to clock time.

Step 1

Look at the sundial time indicated by the shadow. The shadow will be cast on markings for the time of day. Make a note of this number.

Step 2

Adjust for the location within your time zone. Add four minutes to the sundial reading for every degree you live west of the center of your time zone. For every degree you live east of it, subtract four minutes.

Step 3

Adjust for daylight-saving time. If daylight-saving time is in force, add one hour to the sundial reading.