I assume you mean the one for mash pH prediction. It isn't very refined at this point. I was giving a presentation on my technique for estimating mash pH and when the previous speaker illustrated his presentation with a spreadsheet I thought 'I should do that too' and cobbled it up during the rest of his talk. I've added a few things since then, though. It's at http://wetnewf.org/pdfs/Brewing_articles/MashpH.xlsx and be sure to download the slides from my presentation so you'll understand how it works. It's really great for showing you which parts of your mash contribute and absorb protons.
Don't get too excited about razor sharp pH predictions though. If I make a test mash with malts for which I have complete data it works really well, unsurprisingly enough. But if you try to use it to predict mash pH with a malt I haven't measured in detail you can get results that are way off. This whole thread is built on an unreasonable prediction, based on malts of the same color that I have measured, of mash pH by Bru'n water which obviously bases its prediction on different malts.
As I've only measured 4 malts at this point there aren't many beers you can model. To allow you to play around a bit I have taken Kai Troester's data and derived the average buffering capacity over the range he measured. You can use this as an approximation to the first of the three coefficients my model requires and probably get a fair prediction in many cases. You can even interpolate values of this first coefficient between colors as given in Kai's data but there is no reason to expect that the prediction will be any better than any other one that tries to do this based on malt color.
Put another way, my model is robust but the data you will have to put into it, other than for the 4 malts I have measured, isn't. So at this point I really think the value is more in that it will show you about where the protons flow than in its pH predictions.