Determining fluid flow from circular pressure diagrams
Notes: "A square root planimeter measures circular charts that show pressure (from a pitot tube) that is in a fluid flow. Knowing the size of the pipe the flow rate can be derived from this. It is used much as a radial planimeter, with a peg stuck in the middle of the chart, and the tracing point moved around, following the data trace. The curved slot that rides on the pin provides the square root function. This planimeter is specifically for Barton 1A1 type charts."