Okay, I'll be the first to admit I'm more adept at Flow than Simulation, so...

I would like to define a new parameter for post-processing.  In a series of simulations I have either tension or compression but rarely any shear.  So instead of using a separate P1 and P3 plot I'd like to make a parameter that is P1+P3.  Not intensity (P1-P3) because that always gives you a postive value, I want to be able to see whether it is tensile or compressive.

So I go to "Add Parameter" and try to input this.  But I can't find a list of the built-in variables you are allowed to use.  All I want to do is P1+P3.  Should be easy enough.

Hints or suggestions?