Sure, it's in the source code:
http://avisynth2.cvs.sourceforge.net...ew=markup#l815
Code:
if (dropframe) {
if (rate == 30) {
int c = 0;
c = off_min + 60*off_hour; // number of drop events
c -= c/10; // less non-drop events on 10 minutes
c *=2; // drop 2 frames per drop event
offset_f -= c;
}
else {
// Need to cogitate with the guys about this
// gotta drop 86.3 counts per hour. So until
// a proper formula is found, just wing it!
offset_f -= 2 * ((offset_f+1001)/2002);
}