An appendix to my essay to gunnery : Or, distances and heights may be found accessable or inaccessable one mile two or three without the help of geometrical protraction. Arithmetical or trghonometrical calculation. By a small instrument in the form of a two foot joynt rule, with a slider and sights, fitted to any mean capacity, that knoweth little of either writing or reading. And for those that are more learned, there is a secter line of cords to 180 degrees, by which all angles may be taken, either for distances of surveying, and a tangent line for altitudes, shewing more at large the multiplying of fractions and the rules of practise in decimals, with the way of extracting the square root. Invented, published, and the use thereof taught by William Walgrave dwelling at the two White Posts in Newton street near little Queen street in St. Giles's in the Fields. The instrument is made and sold, and the book shewing the use thereof, by Mr. Walter Hayes near the Popes Head Tavern in Morefields, London. - Walgrave, William. (printed by H. Brugis for the author and R. Pyne,, 1681)