It has no value. It is purely used in the formulas, as described in the project description (in particular on page 12). If you try to use it to compute anything, that should be rejected by the type checker.
By applying the formulas from the project description (in particular the one on page 12) or from the script (they are the same).
If a k is present, then this variable is used as k, otherwise, you make one up.