The mechanical log recorded the speed and distance run by a ship, which was vital information in recording daily progress. It worked by being thrown overboard and dragged behind the ship. As it was dragged along, the log rotated and the revolutions registered on the dials on its side. This example is made of brass with an enamel plate for the three dials, which are marked in miles from 0 to 100 in tens, from 0 to 10 in units, and from 0 to 1 in quarters. Each of the five fins at the back is inscribed with an anchor above the letters 'T W' (for Thomas Walker).

From the 16th century onwards people had made many attempts to devise a mechanical log which would automatically record speed or distance, but it was only in 1802 that the first commercially successful version was patented by Edward Massey (1768-1852). It consisted of a brass rotator linked to a geared mechanical recording mechanism. Massey's design was further refined by Thomas Walker (1805-71) and his son, also Thomas (1837-1921), who took out a patent for the A1 Harpoon Log in 1861. When acquired, this example had a wooden stand that recorded that it was 'Taken from German drifter "AUE" North Sea 6.8.14'.