Making plots with separate y-axes

[Kevin Hill]

Hello everyone,

I am trying to plot time-series of minimum sea level pressure for two
different simulations, along with a line showing the difference between
the two. I would like the minimum pressure values to correspond to one
set of y-axis values (say 900 - 1000 hPa, shown on the left side of the
plot), and the line showing the difference in sea level pressure to
correspond to another set of y-axis values (say -10 to 10 hPa, shown on
the right side of the plot). So far I have not encountered any way to do
this type of plot with grads; can any of you provide assistance in how
to do this? I know I can do it using other programs (even Excel), but
would like to do this with grads if possible.

Thank you,

Kevin