I set this up a few years back as I have a basement darkroom in a cold climate that requires a bit of extra tempering before I can get to my projects. I just added some higher temperatures and made certain it worked in that direction, too. A friend also found it useful and that me think that it could be handy for others who aren't spreadsheet experienced or who would appreciate saving the time to do it themselves. It's in Excel format: http://chibardun.net/~craigclu/TempBlender.xls It seems to be without error but if you spot anything, let me know and I'll correct it. I've learned to add a fudge factor for the vessel mass and its effect on the tempering but this is a quick way to get dialed in and save time.