Suppose remote = 3.0 and local = 1.0. This formula will calculate the mismatch "ratio" to be: abs (2.0 * (remote - local) / (remote + local)) == abs (2.0 * (3.0 - 1.0) / (3.0 + 1.0)) == abs (2.0 * 2.0 / 4.0) == 1.0 If remote instead equals 0.33 we get the same mismatch ratio: abs (2.0 * (remote - local) / (remote + local)) == abs (2.0 * (0.33 - 1.0) / (0.33 + 1.0)) == abs (2.0 * 0.66 / 1.33) == 1.0 This example demonstrates how the formula is both symmetrical and invariant in the scale of the parameters. ie. swapping remote and local, or scaling them both by a constant factor, will produce the same mismatch ratio. See this wikipedia entry for more info on ways of calculating relative differences: https://en.wikipedia.org/wiki/Relative_change_and_difference