# Can you measure the area of a shape with a ruler and a bent coathanger?

This youtube video video from How Round is Your Circle? claims you can estimate area with a tool created from a bent coat-hanger.

I am a little skeptical about the claim which is why I am posting this here as opposed to math.se.

Is this really a way to measure area, and if so what is it called (and maybe why it works)?

• It is now crossposted to Math.SE. Jun 16, 2011 at 0:41
• Planimeters are among those instruments that have to be seen to be disbelieved. They come in several varieties and can be staggeringly beautiful. A dear friend gave me a good one for my thirtieth birthday and it has pride of place among my office display pieces---yes, even ahead of my slide rule and artillery spotter's calculator. Jun 16, 2011 at 1:21
• @picakhu -- hi picakhu. Pika, pika! :) Based on your comments below you seem to "not believe" that a planimiter is a completely normal everyday real instrument. You can easily buy one say here engineersupply.com/… or here amazon.com/Lasico-MECH-POLAR-PLANIMETER-ENG-CAL/dp/B001E0FHCQ. You can see many photos of it here ... en.wikipedia.org/wiki/Planimeter (Of course, the "cheap" planimeter in the youtube video would not be very accurate.) Yes, it is a totally normal thing. They are used every day by draftsmen. Jun 16, 2011 at 13:12
• @Bill Tags don’t have to be specific; tags should be general enough to group subjects into categories. The tags suggested by you don’t really do this. I think even in a few years the number of questions about “measuring-devices” can be counted on one hand. Jun 16, 2011 at 16:22
• @konrad: Speaking as a mathematician with decades of experience in math and computation, I've encountered much skepticism about the correct function of various analog computational devices. So I wouldn't be surprised to see more than a handful of such questions here over many years time. Why throw away expert-contributed knowledge (here tags) that could later prove difficult to duplicate? Jun 16, 2011 at 16:51