Thomas Walker died in 1871 aged 67, leaving his business in the hands of his son Thomas Ferdinand Walker. The younger Walker made a further fundamental improvement to the design of the Walker Harpoon Log by taking the dial out of the rotator and installing it remotely, on the side of the ship. First known as 'Walker’s Taffrail Log’, it became officially named the ‘Cherub’ log.. The Cherub log was designed so that the log did not have to be hauled in every time a reading was required – a highly significant development. Production of the Cherub log started in the 1880s with 400 sales in the first year, by ten years later they were selling around 2,000 per year  In 1902 a further improvement was made: the Walker Electric Log, designed so that the log could be read from various sites on the ship, including the ship’s bridge. An important improvement made to the Walker logs was the use of a small impeller on the boat's hull below the waterline. This enabled the distance travelled by the ship to be calculated without the need to manually place a log in the water each time. As well as ships logs, the company manufactured depth sounding instruments including the Harpoon Depth Finder. The instrument is lowered to the seabed and the rotor turns, rotating dials showing the depth of water. The rotor is free to rotate as the instrument is lowered, but when the line is drawn up a locking piece drops down and holds it in place. The lead weight has a depression in the bottom into which wax can be poured. By examining the wax, the sailor may be able to identify the nature of the seabed, for example, if it is sandy. In 1905 the company was incorporated as a limited company (Ltd). The firm was based at 58 Oxford Street, Digbeth, Birmingham. The factory was built for Thomas Walker & Son by Buckland & Farmer of Birmingham in 1912. It is a Grade II 'Listed building'. In 2002 Lilley & Gillie Ltd, manufacturer of magnetic compasses, acquired Thomas Walker & Son Ltd (Walker Marine), adding Walker's electromechanical speed logs and anemometers to the firm's list of products. The name continued to trade, as it had since 1838, under the brand name Walker Marine.