The sextant tester consists of a black-lacquered brass and cast-iron frame, with a vertical sheet of brass with a hole at each end. There is also an artificial planet and star used for testing the measurement of a fixed distance at different position angles. The small hole is for a star, the larger for a planet. Two supports for candle lamps are both missing. The vertical sheet is mounted and pivots on a vertical cast-iron column that is set on a cast-iron base with three feet.

In use the image of the star is made to touch the image of the planet by adjusting the sextant from a fixed distance. The angular measurement should be the same on all sextants thus tested. A label stuck on the back of the vertical column is marked ‘R.A.S., No.96’.

John Browning worked at 111 Minories in London, from about 1864 to after 1900.