To make a dial that correctly tells standard time you will need to know your latitude for dial construction and longitude to determine the correction (time zone offset) between your dial and the time zone meridian (usually set every 15 degrees of longitude).

IMPORTANT Some maps will indicate longitudes in North American as negative, indicating that they are west of Greenwich.  Other maps will indicate longitudes in North American as postive, declaring them "west longitude".

Correcting for your position in your Time Zone

When solar time became inadequate for railway timekeeping, a system of time zones was initiated creating 24 time zones, each 15° wide - within which zone all clocks would tell the same time. (Basic arithmetic: The earth's 360° circumference was divided into 24 one hour segments, and the result was 24 time zones each 15° wide.)

This correction for your sundial is determined by the relationship between the longitude of your sundial and the longitude of your time zone meridian. The central meridians of all 24 time zones can be found in the table below. Note: some time zones are perturbed by geographical and political boundaries.

The correction is the difference between your longitude and the time zone meridian, converted into minutes. For example: