public void setRangeIndex(@NonNull final String var, final int rangeIndex) {
        final VariableState state = variableStateMap.get(var);
        if (state == null || state.rangeIndex == rangeIndex) {
            return;
        }
        state.rangeIndex = rangeIndex;
        recalculate(var);

    }
Adds or changes a variable - formula assignment to this map.
<br>
Note that on adding/changing a variable's formula, the map will ensure that for all
variables where the formula depends on there will also be an entry in this map (state might be empty though)
main/src/main/java/cgeo/geocaching/utils/formulas/VariableMap.java