A schema for horizontal dials is a set of instructions used to construct horizontal sundials using compass and straightedge construction techniques, which were widely used in Europe from the late fifteenth century to the late nineteenth century. The common horizontal sundial is a geometric projection of an equatorial sundial onto a horizontal plane.

Mario Bettinus was an Italian Jesuit philosopher, mathematician and astronomer. The lunar crater Bettinus was named after him by Giovanni Riccioli in 1651.