Wayne, The reason that most of them are flat are due to the fact that they just don't exchange over the course of the experiment (0 to 85 hours), so a flat line would be expected. There are a few that exchange over the time course of the experiment and they have nice fits to the exp. decay. This is all good news on my front. Looks like the error was fixed with the last update. Thanks for your help and now we have one less bug to worry about! -J