This instrument is a recorder for determining distance travelled and thus ship’s speed. It is made of brass with a ceramic dial, with the main scale marked from 0 to 100 miles and two inset dials marked from 0 to 1000 miles and 0 to 1 mile. It has a fixing plate, on which it can turn, with which it would have been attached to a suitable part of the ship, typically the taffrail, the rail at the stern of a ship. As a result, this type of log was often called a taffrail log. The recorder would have been connected to a rotor that was towed behind the ship. The revolutions of the rotor registered on the indicator, thus measuring the distance travelled. For this model, 900 revolutions of the rotor registered as 1 nautical mile.

Thomas Ferdinand Walker (1837–1921) first patented the Cherub log in 1878 (no. 4369). It was one of the first logs in which the recorder was placed on board the ship rather than being part of the rotor. The Cherub Mark III series proved to be very successful and was produced in great numbers between 1930 and 1994.