Sundial Correction Calculator

You may have been frustrated that when reading a sundial, it doesn't give the same time as your watch.

This is because sundials show the local solar time, whereas clocks show local mean time, aka 'clock time'. A correction is necessary to convert from one to the other and this depends on your location and the time of year.

Knowing this correction will let you show that a sundial does really work. Alternatively, you can use it to check if a sundial is set up correctly.

When sundials were in more common use, the necessary correction was originally applied to clock time to get the 'real' solar time, but nowadays the clock time is considered the 'real time', so the adjustment must be applied to the sundial's time instead. This app will show you the correction to apply to the sundial's time.