He devoted his leisure to the study of mathematics and merchants' accounts, and on leaving the service set up in London as a teacher. In 1652 he published "An Introduction to Merchants' Accounts", originally drawn up for the use of his scholars. Reprinted in 1665, the major part of the impression perished in the great fire of London, but was replaced in 1674 by a new and amplified folio edition. He next wrote "The Sector on a Quadrant, or a Treatise containing the Description and Use of three several Quadrants." Also an appendix touching "Reflected Dyalling, from a Glass however posited" (London, 1658); and "The Description and Uses of a general Quadrant, with the Horizontal Projection upon it Inverted" (1658). In 1659 appeared his "Geometricall Dyalling, or Dyalling performed by a Line of Chords only", and "The Mariner's Plain Scale new Plained", a treatise on navigation for the East India Company's navy. It was well received, and became a class-book with the students of navigation at Christ Church Hospital.