Determining mean value on circular recording charts
Notes: "The Model 4215 radial planimeter was in the K&E catalogs from 1921 until it's name was changed to 62 0100 in 1962. This appears to be a later one, probably from the 1950's, due to the modern style K&E logo on the planimeter's frame. Both the pin and pin remover are included. The pin would be stuck in the middle of the chart being measured and the planimeter would pivot around it. The spring steel pin remover makes extracting the pin from the drawing board easier."