A horizontal dial’s gnomon must sit in the plane of the Earth’s axis. Its style angle equals the site’s latitude. Hour-line angles follow tan(H) = sin(φ) · tan(t) where t is the hour angle. The bench does not correct the equation of time.
Formulae: Waugh, Sundials; British Sundial Society primers. Longitude offset from the time-zone meridian is 4 minutes per degree — add it by hand. Summer time is a political hour, not a solar one. Polar dials and vertical declining walls need more than this plaque.