There are a variety of situations in which it may be desired to examine rock properties along a contour for some property of a phase or the system (a mineral mode, a mineral composition, volume, entropy, enthalpy, seismic velocity, etc). Such constructions are relatively simple in Perple_X and involve three steps:
Computation of a phase diagram section (usually pressure-temperature) with VERTEX.
Extraction and refinement of the contour coordinates with WERAMI and PSCONTOR (this can be done more efficiently using the griddata function of MATLAB, see the Perple_X script pt2sv for an example).
Extraction of the properties along the contour with WERAMI and graphical display with PSPTS or PT2CURV/PSVDRAW.
This can be done for any property that can be extracted with WERAMI. A specific calculation is outlined in the "adiabatic crystallization tutorial", wherein mineral and melt modes are computed along a constant entropy contour for decompression melting.