English mathematician known for his applied work in navigation, surveying, and ballistics. His almanac (1555) contained much useful information for sailors. In 1556 he published Tectonicon, a manual of elementary surveying techniques. Pantometria, published posthumously by his son Thomas in 1571, was a manual of practical mathematics that contained more advanced and up-to-date surveying techniques. Digges also invented the theodolite, a portable instrument for measuring horizontal angles.