Determining Mean Effective Pressure from indicator diagrams
Notes: "This is a very early Willis planimeter, from before the ""Improved"" model came out after the 1896 patent. Only the 1894 patent is shown on this one. The biggest change is in how the tracing wheel moves. On this early one, it slides on a glass rod. Later versions have the tracing wheel rigidly attached to a metal rod that slides through the frame, and even later models give the wheel ball bearings to ride on a triangular rod. This planimeter came from the factory with the optional horsepower attachment, which is included."