Be sure the spot you've chosen is level and in full sun. If you have picked out a 'vertical' sundial, it should be mounted on a sunny, south-facing wall. Place your sundial so that the gnomon (the shadow arm) is pointed toward celestial north. Reset or set your sundial on April 15, June 15, September 1 or December 24. If you set a sundial on other dates, it can be as much as 14 minutes behind clock time or 16 minutes ahead of it. To a sundial, noon is always when the sun is highest in the sky.
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