Re: OpenSCAD Digest, Vol 2, Issue 18

you can either set the number of faces directly by doing this:

$fn=100;
cylinder(h = 10, r = 20, center = true);

or more elegant:
cylinder(h = 10, r = 20, center = true, $fn=100);

or you can use the combination of $fs and $fa ($fs is in mm and $fa in degrees):

$fs=0.5;
$fa=5;
cylinder(h = 10, r = 20, center = true);

greetings
Philipp