Notes: "The System Pregèl is perhaps the most interesting variation on the hatchet planimeter. Instead of a knive edge, it has knife-edged wheels that roll over the paper, without cutting it. There is a push button to make a mark in the paper at the start and end of the trace, and the effective length of the tracing arm is adjustable. It even has a round ball that slides on the paper, keeping the tracing point from scraping across the paper. While all that makes for a spectacular hatchet planimeter, it misses the point that the hatchet planimeter was supposed to be much cheaper than a polar planimeter, while giving up some accuracy. This hatchet planimeter has more parts - machined parts! - than some polar planimeters. This one is serial number 660."