I have a number of different ideas on additional functionality that I'd like to add to WinPCD over time. One of them is additional graphing tools. I started to add a multi-file measurement display tab, but decided that rather than add to WinPCD as a tab, it would be almost as easy to make a free-standing tool.
WinGraph is that tool. It allows a separate window to be open for comparisons of measurement files, both SPL and impedance. You can import and display any number of files simultaneously. I don't know what the limit may be, it's not limited within the program code itself. All files imported are displayed with the full filename in the legend at the bottom.
You can import raw driver files or design output files. If you want to compare designs, you can export them from any software package that puts it into the FRD style output. WinPCD has an export option on the system graph. Once exported, go to WinGraph and import it. It's that simple. The scheme is the same as it is for the graphs in WinPCD. Right click on the graph to pop up a context menu of controls for the graph. You can zoom, pan, display a section highlighted with the mouse (draw a box shape of that area with the cursor), display data points on the curves, etc. The window is fully resizable.
It's available at the main SpeakerDesign web page http://www.speakerdesign.net/.