Thanks, I really appreciate the information. I haven't ever had trouble like this before where I really had NO idea what I needed to do. Even with the notorious AB products where they spread the necessary information throughout multiple reference sources. This is a really old PV, I am trying to standardize my plant anyway so even though it will take a bit of extra work I think I may just replace the stupid thing with a PV+ 600. I know they don't make that 550 anymore but also it seems to be hard to find even old or used surplus of the thing. Thanks again for the help.