A planimeter is a mechanical instrument used to compute the area of a planar region.  Here are some examples.
Polar Planimeter Linear Planimeter Prytz or "Hatchet" Planimeter

How polar and linear planimeters are used.
How planimeters work.
Using a planimeter to prove the isoperimetric inequality.
A Plethora of Planimeters!

Other Planimeter Web Sites
  • How to Use A Planimeter
  • Larry's Planimeter Platter

    Historic Information & Photos of Antique Planimeters

  • The Museum of HP Calculators -- Several good photos

    Mathematical Details

  • The Computer Museum
  • Whistler Alley Mathematics: The Planimeter
  • Planimeters & Green's Theorem
  • Antique Dealers and Auctions That Often Have Planimeters

  • The Gemmary Antique Scientific Instruments -- This is a great site with excellent photos
  • eBay Search for "planimeter" or click on "Antiques" and then "Science Instruments."
  • Companies Selling Modern Planimeters

  • Lasico
  • ASC Scientific
    It is not my intent to support any particular manufacturer or seller of planimeters, only to illustrate that they are still being made. Modern electronic planimeters are typically expensive, however, in my opinion, the electronics are illusory. They are mechanically the same as their non-electronic ancestors, just with a calculator riding piggyback. The scale is read electronically, and the results can be read out in square inches, square centimeters, or (based on the scale of a map) square miles. Some also measure the perimeter of the region. They are not noticeably more accurate, since their accuracy lies in the skill of the operator, not in the electronics.

    Try using one of the web search engines to search for "planimeter."  You will get lots of "hits," most of which will illustrate the variety of ways planimeters are used in science, technology, medicine, archeology, and many more areas.

    Last update 24 August 2007
    Robert Foote