Planimeter

A planimeter was invented by the Swiss mathematician Jacob Amsler in 1854. It is a mechanical device used for measuring areas of irregular shaped surfaces. Planimeter needs plan drawn on the sheet to calculate area. Accuracy of results is dependent on the size or scale of the map. The bigger the scale of the map, the more accurate the area will be.

Typical applications include the area measurement of irregular geographical regions on maps or features on enlarged photographs of biological specimens.

Following are the parts of a planimeter:

1. Tracing arm: Tracing arm is an important part of planimeter it manages the position of tracing point at one end with the help of hinge.
2. Tracing point: Tracing point is the movable needle point which is connected to tracing arm. This point is moved over the outline of area to be measured.
3. Anchor arm: Anchor arm is used to manage the anchor position or needle point position on the plan. It’s one end is connected to weight/ needle point and another end to the integrating unit.
4. Needle point: It is also called as anchor. A fine needle point is located at the base of heavy block.
5. Clamp: Clamp is used to fix the tracing arm in standard length without any extension.
6. Hinge: The tracing arm and anchor arm are connected by hinge to the integrating unit. With the help of this hinge the arms can rotate about their axes.
7. Tangent screw: Tangent screw is used to extend the tracing arm up to required length.
8. Index: Index is a location where all the measuring arrangements like wheel, dial are located.
9. Wheel: Wheel is fixed in the integrating unit which helps to measure the tracing length. It is used to set zero on the scale.
10. Dial:  Dial is nothing but scale, before taking a measurement dial must be set at zero point.
11. Vernier: Vernier of planimeter is a metal bar which has engraved graduation like Vernier caliper. It is divided into 100 parts.

How to Find Area using Planimeter:

• Anchor point/Pole arm is to be fixed at one point. If the given plan area is small, then anchor point is placed outside the plan. Similarly, if the given plan area is large then it is placed inside the plan.
• Secondly, place the tracing point on the outline of the given plan using tracing arm. Mark the tracing point and note down the reading from Vernier as initial reading A.

• Now move the tracing needle carefully over the outline of the given plan till the first point is reached. Note down the reading on Vernier after reaching the first point and it is the final reading B.
• The movement of tracing needle should be in clockwise direction.
• Now you have two readings. Put the readings on specific given formula to calculate the area.
  • M (B – A + 10N + C)

Where:

1. A is initial reading.
2. B is final reading
3. N is no. of revolution of wheel on one complete tracing.
4. M & C is constant values are given on planimeter

https://www.youtube.com/watch?v=jMvEOmpy8Kw

Online Purchase:

The price of a planimeter normally ranges between 40-60 dollars in international markets.

https://www.ebay.com/itm/Dietzgen-Compensating-Polar-Planimeter-with-Manual-and-Case-Model-1810-/323590623536

https://www.ebay.com/itm/EUC-Keuffel-Esser-Co-K-E-Model-620005-Compensating-Polar-Planimeter/173702843003?hash=item28717f0a7b:g:uRMAAOSwXHxcHabc:rk:23:pf:0