[R] plot - labels in axis doubt

[javier garcia - CEBAS]

Hi all;
I need to add lines to a plot and an additional axis in the right side with a 
specific scale for this second serie of data. I've seen once this but I can't 
find it now nor can manage to do it. The tickmarks can ve the same that the 
default left axis, but how could I indicate the labels?
Let's say the left scale ranges from 0 to 100, and I need to say that the 
second scale is a specific ratio to this one (because I've choose that ratio 
between the max value of both series to multiply the second, and so be 
adapted to the plotting space of the first plotted serie)

Can someone tell me about any example? 

Thanks and best regards,

Javier