Talk:Planimeter

message: Is it correct to say (or write) that a planimeter is a drawing instrument, while no one can draw with a planimeter? It is a measuring instrument, is it not?! — Nol Aders 23:41, 17 December 2005 (UTC)
replies: text: Perhaps, while it cannot draw, it aids in the tasks of technical drawing? Melchoir 13:48, 5 January 2006 (UTC)
thread_title: Measuring, not a drawing instrument?!

message: The application of Green's theorem lacks two things. a) It doesn't say whether it is a linear or a polar planimeter. b) The result is not relevant. Integration of (-y,x).(dx,dy) is not what the planimeter does!Nijdam 15:47, 2 July 2007 (UTC)
thread_title: Green

message: The more basic formula which forms the basis of the planimeter operation is Leibnitz's sector formula which preceeds green's theorem by about a century. Setreset (talk) 05:48, 17 November 2009 (UTC)
thread_title:  basic formula  

message: I may be missing something but it seems to me that the reference to Green's theorem in the subsection 3.1 titled "Polar coordinates" doesn't make sense. The area integral in polar coordinates makes sense, but if I follow the reasoning, you are integrating \scriptstyle \int_t r(t) \cdot \dot \theta(t)\,dt, (the derivative of the area function) along the perimeter. Green's theorem says
:\int_{\partial R} \omega = \int_{R} \mathrm{d}\omega
Essentially this argument is doing
:\int_{\partial R} \mathrm{d}\omega
So you'd need to be integrating the antiderivative of the area function \int_t \tfrac{1}{2} r(t)^2 \cdot \dot \theta(t)\,dt. along the perimeter, not the derivative of it. I might be missing the right interpretation of this, though. Ofb (talk) 03:18, 20 March 2012 (UTC)
replies: text: I recommend you check out this paper, fix it up to agree, and cite it.  Dicklyon (talk) 05:55, 20 March 2012 (UTC)
thread_title: Reference to Green's theorem in the "polar coordinates" section doesn't make sense?

message: In case someone wants to make a (needed) section on the Prytz Planimeter before I get around to it, I found a decent technical article with history from the 1908 American Mathematical Monthly. Available on Jstor here: .  Sill looking for a free photo.  --Theodore Kloba (talk) 21:03, 25 March 2014 (UTC)
thread_title:  Hatchet (Prytz) Planimeter Suggestion 

message: You have 
\iint_D(\frac{\partial{x}}{\partial{x}}-\frac{\partial{(b-y)}}{\partial{y}})dA=\iint_D dA
however 
\frac{\partial{x}}{\partial{x}}=1
and 
\frac{\partial{(b-y)}}{\partial{y}}=-1
and 
1-(-1)=2,
so the equation should read
\iint_D(\frac{\partial{x}}{\partial{x}}-\frac{\partial{(b-y)}}{\partial{y}})dA=\iint_D 2dA
In other words, the integral gives twice the area.
ZacharyFoj (talk) 21:21, 15 December 2014 (UTC)
replies: text: Quantity b is the y-component of the elbow, so b is a variable and not a constant; partial(b)/partial(y) not zero; see text below equation. Glrx (talk) 20:57, 17 December 2014 (UTC)
replies: text:  True, but since we are talking about a partial derivative I thought it didn't matter....ZacharyFoj (talk) 05:59, 27 January 2015 (UTC)
replies: text:  On further inspection, I've found my error. Thanks! ZacharyFoj (talk) 06:03, 27 January 2015 (UTC)
thread_title:  I think the integral is wrong.... 

message: The CIA’s cartography department put up some nice photos of planimeters, e.g. https://www.flickr.com/photos/ciagov/30764630562/sizes/ and https://www.flickr.com/photos/ciagov/30792301801/sizes/ etc. in a whole set https://www.flickr.com/photos/ciagov/albums/72157674852500522. Someone may want to upload a few of those to wikimedia commons and include them here. –70.36.196.50 (talk) 10:25, 12 February 2017 (UTC)
thread_title:  nice CIA photos of planimeters