B62-50. ACOUSTIC CURRENT METER. Price Patent. Patented 1897 by William Price of Chicago and used to measure the current of rivers and canals. You lower it into the water where the current turns the cups and causes the shaft to rotate, with a clicking mechanism that you listen to through the flexible tube. Looks clean and complete and ready to use, in a box that's rough but complete with "Hydrography USGS" stamped into outside of lid and some water-stained instructions pasted into the inside. Good+ 60-120