↑ "Echo Sounding / Early Sound Methods". National Oceanic & Atmospheric Administration (NOAA). NOAA Central Library. 2006. In answer to the need for a more accurate depth registering device, Dr. Herbert Grove Dorsey, who later joined the C&GS, devised a visual indicating device for measuring relatively short time intervals and by which shoal and deep depths could be registered. In 1925, the C&GS obtained the very first Fathometer, designed and built by the Submarine Signal Company.
