CF Chart - line graph - use non-numeric values in the y-axis, eg "a, b, c"

I am trying to print a line graph using CF Chart. I want to use non-numeric values in the y-axis, eg A, B, C, D etc or bad, good, very good, excellent etc.

I have no problems with numeric values.

If it cannot be done, I would at least like to display the y-axis labels as non-numeric at the scale points and use a numeric substitution for positioning.