Planimeter is a Surveying instrument which can be used to find out the area of a map or plan. A Swiss mathematician Jacob Amsler Laffon built first modern planimeter in 1854. Many developments followed Amsler's famous Planimeter including the electronic planimeter.
|A Polar Planimeter (source: wikipedia)|
- Hatchet Planimeter
|Linear Planimeter (Source : Wikipedia)|
In order to find out the area, all you have to do is to trace the perimeter of the area on the map, and note down the reading.
To get more accurate results one should be skilled in tracing the exact perimeter of the shape.
You can convert the area to the field area using the scale of the map.
These days digital planimeters are in the market which are more easy to use.