This calculator calculates uncertainty of ReturnLoss and VSWR given coupler directivity.
The calculator does not do a lot of error checking, if you enter nonsense, it will produce nonsense. NaN means not a number, check the input values.
VSWR must be greater than 1, Return Loss must be +ve and directivity must be +ve. If input VSWR or ReturnLoss is inconsistent with Directivty, then no results are shown.