Interpolation is a method of constructing new data points within the range of a discrete set of known data points.
This is the perhaps the best app on App Store for interpolation and extrapolation calculation.
The app uses two methods
1. Linear Interpolation
2. Polynomial Interpolation
Linear Interpolation is free to use.
However you have to purchase the upgrade in order to access polynomial interpolation.
We intend to add more features to add. So do let us know if you have any suggestions.