Area meter - Area meter

Also known as a planimeter, this is an instrument used to find the area of ​​a figure surrounded by curves. In the diagram, there are two movable arms, AC and DC; if D is fixed to a point outside the figure on the drawing and the tip of A is made to rotate once along the curve of figure B, the small wheel E will rotate due to friction with the paper surface. The number of rotations G and angle of rotation E are read from the vernier scale at F, and this is multiplied by a coefficient to find the area. The coefficient changes depending on the length of AC, so the precision can be altered.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

プラニメーターともいう．曲線に囲まれた図形の面積を求める器械．図でAC，DCの2本の可動な腕があり，Dを図面上の図形外の1点に固定し，Aの先端を図形Bの曲線にそって1周させると，Eの小車輪が紙面との摩擦により回転する．その回転数Gと回転角Eの目盛をFのバーニヤスケールから読みとり，これに係数を掛けて面積を求める．ACの長さによって係数がかわるので，精度をかえることができる．

出典　森北出版「化学辞典（第2版）」化学辞典 第2版について　情報