How to show values on the right Y axis

I notice that the graph axes allow you to show left and right Y axes:

My hope is to show a few lines, some with a percent measurement (left axis) and one with a distance measurement (in mm, shown on right).

The right-Y axis label is shown, but the scale (i.e. the numbers up the side) are not. Is this normal? How do I get the right-Y scale to show?