This instrument is designed to measure the distance covered by a ship. In this design, a brass rotor trails in the water and spins around as the boat moves along. This rotary motion is then passed through a set of linked brass rods to the register. There are four dials on the front of the register and one on the back giving a readout of the distance travelled in nautical miles and feet. This form of log was patented by Edward Massey (about 1768-1852), whose name is inscribed on the register, along with the trademark of three Ls in a triangle.
Original instruction label pasted in lid of box, now in sling file.