Hey thanks for the link.

So it appears Park has no problem making the generalizations I have above; the simple equation even ignores Trevor's point about the slope of the chainline, while I think that the "rigorous" equation corresponds to what I put up.

But what's up with the +1 that they throw in there? A fudge factor to make sure you don't cut too short a chain? Or maybe I'm missing something.

[edit: Oops, didn't read the fine print. They in fact suggest for s/s bikes that you eliminate the +1]