Sorry for gbeing away. Real life intervened. The graphs are done using Visifire. PSA is indeed prostate specific antigen. This tool works for any value though, and is designed to look at biomedical data. As you point out the doubling rate, or just the rate of increase is a massively useful value. By plotting a log rate, it makes the graphs easier for us, but risks making them more difficult for the end user. I was planning to open source all of this as soon as I got it into a fit state for others to understand.