The planimeter is used for finding out areas of irregular figures on sheet there is a number of formulae available for calculating areas of regular figures, but the actual problem arises when the figure is irregular.
Planimeter of conventional type like Amsler polar planimeter, rolling planimeter etc, require a lot of time for the setting of the farcing arm scale etc. to overcome this, on electronic digital planimeter is used nowadays to obtained the areas of irregular figures directly, accurately as well as quickly, which saves a lot of time and labor.
Digital planimeter works on the built-in nickel-cadmium storage battery.
There is a rotary encoder, which has replaced the integrating wheel by mechanical planimeter. An electronic circuit measures the pulses of rotary encoder and area is displayed in digital form.