I would go for a google search on that function.
I seem to remember that there were some dodgy stuff about the statistics functions of excel (or there used to be pre 2000). Matlab is the way forward,
A mate of mine found this out when he submitted his Phd and had to go back a redo all his statistics again. Thankfully he was working on steel so had gnats cock sized errors in the grand scale of things so didn't alter to much.