Reading clock time on a sundial requires three major adjustments to the solar time displayed: adjusting for the reader's location, for Daylight Savings Time and for the non-uniformity of solar time. The sundial shows the local solar time of a given place, which is the time measured by the sun.
The golden rule for adjusting the solar time to reflect location states that one must add 4 minutes to the sundial reading for every degree of longitude that a person lives west of the center of a time zone. Those living east of the center must subtract 4 minutes for each degree. To read a sundial when Daylight Savings Time is in effect, one must add 1 hour on the sundial time to get the actual clock time.