Keith (or anyone else who knows),

I'm looking at the facing curve spreadsheet that you have under 
the Files section (FacingCurve.xls), and I have a few questions:

1) R - what does this represent? (The Radius of the curve?)
2) M - not sure what it stands for, but it's obviously the facing 
length
3) Spec (specification? WHat is this, and what does it represent?)
4) Diff - difference? between what?
5) L Inc - I think I have this one: Length Increment, correct?

Questions on Usage:
"Adjust M until L at Tip = 0".
I'm not sure what M is? Is this spreadsheet to be used for plotting a 
facing that I've measured from a mouthpiece, or is it for determining 
the feeler gauge points for a facing curve that I want to apply to a 
mouthpiece?

In other words, let's say I want a facing length of 50 (on the glass 
gauge, which is 25 mm, correct?), with a tip opening of .110.

How do I use the spreadsheet? I adjusted M until L at Tip was zero 
(Length was 58.2 - seems rather too long)

Then I adjusted R to minimize the Error Sum - 7.33 gives an Error Sum 
of 0 (though I really don't know what this is).

But now my L at Tip is -6.1. Unless I adjust M again, but then the 
Erro Sum is off again.

Obviously, I don't know what I'm doing. Are there instructions posted 
somewhere? If this has already been covered in an old post, please 
forgive me, and point me in the right direction.

Many Thanks!

-Pete