The app is useful for specific areas, that use acre, kanal, and marla as measuring units, like Punjab (Pakistan, India).
Here are the units used for Area calculations,
'Sarsai=30.25 squre foot
'Marla= 9 sarsai
'Marla=272.25 squre foot
'Kanal= 20 marlas
'Acre= 8 kanals
App is used for calculating the Area of rectangular or square fields.
Calculations are accurate for the farmers. Do not use it for calculating commercial plot area. It is useful for plots, which have small differences between their parallel lengths.