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Sundial AccuracyThe author has dreamed about building the ultimately accurate sundial for some years. However there are a few challenges to overcome before a sundial could be consistently accurate at the level of the second.By providing some way for observers to correct for Equation of Time, sundial makers regularly achieve +/ 1 minute accuracy in their dials when compared to UT. What are the factors that limit sundial accuracy?
Fundamental problemHowever the most fundamental problem for accuracy of the sundial is the:
The graph shows the difference between Equation of Time during 20022005 and long term average values for each day of the year. You can see that the variation is +/22 seconds of time. The long term average values for Equation of Time were chosen to give optimal values (i.e. minimum error) over the 21st century. As you can see from the graph, if a sundial's equation of time correction will give 'good' results for over the long term, the sundial will have errors up to +/ 22 seconds of time during 20022005. Calculate it!The Sun API provides the sdxEOT function for calculating Equation of Time. 

(c) 20012015 Sunlit Design www.sunlitdesign.com Wed, 04 Mar 2015 09:43:27 AM +700 gives UT 