It was typical of the mathematical practitioners, whose numbers were growing significantly in early-modern England, to seek to design instruments to help their clients avoid too much calculation. Here Staynred, 'Professor and Teacher of the Mathematicks in the City of Bristol', explains the geometrical construction of fortifications, the use of tables he provides for calculating their elements, and the construction of an instrument, 'The Scale of Fortification', from these tables. His short tract was printed in London by Mary Clark, and introduced by Samuel Sturmy into his Mariners Magazine (catalogue no. 41). The title-page carries a verse from the Book of Jeremiah: 'The Lord is my strength, and my fortress, and my refuge in the day of affliction'.