How does the Eulers Formula for Planar Geometry Calculator work?

Free Eulers Formula for Planar Geometry Calculator - This calculator solves for any one of the 3 following items using Eulers Formula for planar geometry:
* Vertices (v)
* Faces (f)
* Edges (e)

This calculator has 3 inputs.

What 1 formula is used for the Eulers Formula for Planar Geometry Calculator?

v - e + f = 2 where v = vertices, e = edges, and v = faces