Adding a second y-axis to a plot

Perhaps I've over looked something, but I can't figure out how add a second y-axis to a plot. I'm specifically interested in adding a right hand axis.

I've got a plot of two variables and would like to show their ratio on the same plot. It makes no sense to have the same y-axis for the variables as their ratio because the units are different and the scale is completely inappropriate.

Export the data and then plot in Matlab is the best solution I've found. Is there a better one?


Thanks.

O