If the location chosen for a sundial does not match the its design parameters - the intended longitude and latitude - the sundial will not be oriented in the required way.

For a Horizontal Sundial or any other sundial that stands on a horizontal base, this misalignment can be corrected by placing a wedge under it. The same principle can be used to adjust a sundial to a new time zone even if it stays at the design location.

Use the form below to calculate the shape and postioning of the wedge. If the sundial is an ordinary garden dial designed to show Solar Time, leave the 'Design longitude' blank or set it to zero.


You'll need to convert angles in degrees, minutes and seconds to decimal degrees. Blank fields are treated as zero.

Positive in Northern Hemisphere; Negative in Southern Hemisphere.
Positive to east of Greenwich; Negative to west.
Choose 'Local Solar Time' for a common or garden variety dial (with noon directly in line with the gnomon), or choose the time zone if the dial incorporates Equation of Longitude.
Positive in Northern Hemisphere; Negative in Southern Hemisphere.
Positive to East of Greenwich; Negative to West.
Select 'Local Solar Time' for traditional time by the sun, or select a time zone to get clock time (appoximate, as there is seasonal variation due to the something called the Equation of Time).

Written by Steve Lelievre using principles discussed by Fred Sawyer in an article in the NASS journal, The Compendium 7(1), with additional thanks to Roderick Wall for assistance in dealing with Southern Hemisphere calculations. Offered on a goodwill basis and 'as is'.

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