The app can be used offline using it anywhere.
The calculator program is following electromagnetic theory and transfer matrix theory : Frank J. Pedrotti, Leno S.Pedrotti, by Frank J.Pedrotti, Leno S.Pedrotti., [Introduction to Optics (2nd ed)], Prentice-Hall, Upper Saddle River Publishers, N.J. 391-396, (1993).