Link to why it works
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Overview of Sawyer Equant dial. Photoengraved bronze dial reads local solar time. Sandblasted granite (here African Red) circle reads watch time directly, and is fully adjustable for longitude, daylight savings, and the equation of time. Sundial is 16 inches across the granite.
Side view of Sawyer Equant showing adjustable wedges for setting the dial to the user's latitude. It is adjustable from 23 degrees north, to 51 degrees north, covering the 48 contiguous United States and southern Canada. It is also adjustable for all longitudes.
Close up of dial's face, showing the equation of time scale. The needle is turned to the proper date, and the granite is advanced or retarded by a geared mechanism the appropriate amount for that date. One complete revolution of the needle changes the time by exactly 1 hour, allowing adjustment for Daylight Savings--the needle is simply rotated to the same date, and the granite reads 1 hour earlier or later.
Here is an example of how the dial is read. The bronze face shows local solar time, here reading 4:00 PM. Clock time is read off the granite at the point that the shadow crosses the edge of the bronze, here reading 3:54 PM.
Close up of the wedges (patent 6,301,793), currently adjusted for latitude 44.5 degrees. This design is far more accurate and more sturdy than a traditional protractor-type mechanism.
Prices and Technical Information for Buyers