Gerard Weatherby wrote:

So how many folks in ASA train their crew not to look at the mainsail while
they're "trimming" it?

You mean like with scissors?

Actually, the mainsail trimmer should have a scan pattern, primarily looking at
the horizon and the helm (and the helmsperson's hands: how clenched they are is
a key to what needs to happen with the main). Definitely the trimmer should
look up at the sail, in fact should check several reference points on the sail
(leach ribbons, luff, upper camber, lower camber, etc etc) but should not stare
fixedly at the sail the whole time.

Fresh Breezes- Doug King