Pocket clinometer and square, c 1675-1700.
© Science Museum / Science & Society Picture Library
On the obverse is the clinometer: this consists of two pinhole sights to be used with a quadrant scale which runs along the base and up the right-hand side of the instrument. The reverse carries an unusual form of engraved square for horary and trigonometric uses. There are two sets of parallel lines - one running vertically and one diagonally. The vertical lines are for hours, the diagonal lines represent degrees and are divided as sines. Made by J Marke, a well-known London instrument maker.