For those who wish for an excellent, simple explanation some of the various coefficents and Reynold's Numbers used with airfoils:

http://www.dreesecode.com/other/aflprimer.pdf

It's only 13 pages and is well written.

that is a good read -- and easy to understand
One noteworthy point -- RN under 200000 are typical of models - actually larger models than the crazy micro foamy stuf so popular .
This goes to my own thoughts on airfoils for small - really light ,small high powered models - the airfoil data many espouse as critical for good performance --simply does not apply.
In this realm - weight , area and power are the critical factors .
I only mention this because when I see advice on how to fix a grossly overweight small model - by altering airfoil --I wonder if the advice giver ever flew a small overweight model --
I beat the drum for blaming weight as the only real culprit on these models -simply because any other fix -short of higher speed has not shown much, if any success.
There is a good article in a recent Quiet Flyer mag --developed in a tunnel and dealing with low RN . So far the only tunnel info I have seen which seems applicable to small stuff.

I told a guy on another forum wanting to upgrade a flat-bottomed glider to something better, looking at some Selig airfoils, to go for the cute one.

close enough

Yes, "We" noticed that. "We" are debating if you'll be allowed into the MENSA club room any more...

It should put him at the front of the class--

Mesae,
Great link!!!

.
I bet Ollie and Mark spit out their coffee on that one!

Thanks, I thought so.