Plotting a constant line on a time series plot

[strandwg@xxxxxxxx (Gary Strand)]

I'd like to add a simple, constant value straight line to a plot of a time
series of several quantities. For example, a time series of several model runs'
average sea surface temperatures, and I want to include the mean Levitus
value. The hitch is that not all the model run time series are of the same
length, and, IIRC, it's not easy to specify the begin and end of a time axis.

What I've done up until now is something like:

plot/nolabel sst1,sst2,sst3,sst4,sst5
let lev = if sst1 eq 1.e10 then 0 else 18.39
plot/over/line=1 lev

But that's not real clean if sst1 is much shorter in time than the other four 
runs. 

Any ideas?

PS - It would be nice to have "user" coordinates to "/nouser" transforms, both
directions, readily callable by FERRET, like GrADS does, so one can use geo-
graphic coordinates and the "inches" coordinates on the plotting page 
more-or-less interchangably.
--
Gary Strand                Climate Change Research Section, NCAR (303) 497-1336
strandwg@ucar.edu                          http://www.cgd.ucar.edu/ccr/strandwg