I collect planimeters.
I am interested in how they work, and how and why they were developed.
The purpose of this web site is to share what I know with fellow collectors.
The hope is that some of you will respond in kind, correct any mistakes and fill in some of the gaps.
You can contact me at 
1 Introduction
4 Radial planimeters
5 Polar planimeters (Amsler, Coradi, etc)
6 Polar planimeters (Willis, Lippincott, etc)