Measuring average height of plots on circular charts.
Notes: "This is an unusual radial planimeter in that rather than the planimeter going to the chart, in this case the chart comes to the planimeter. The recording head is fixed, so the chart is placed over the sliding button on the table, and both rotated and slid in and out to keep the data trace under the tracing point. The only movement of the planimeter itself is the recording head, which can be tipped up about 20 degrees to slide the chart underneath it."
