To find the Horizontal Sundial shadow hour angles
for your locality you need to know your latitude.
You can use an online Latitude/Longitude locator,
or in the UK the latitude can be found by reference to
an Ordnance Survey map. This will give your latitude
in units of degrees and minutes.

Convert this angle to decimal degrees using the
Conversion calculator before typing in to the first
box below, i.e. if your latitude is 53° 30', this converts
to 53.5 Then click the calculate button to see the results...