[manigandham]

> Do you think a diagonal saccade is worse than a vertical one for some reason?

Yes, definitely. You don't?

Vertical movement is much easier, just try it. It's also easier to focus since one eye isn't farther away or blocked by your nose.

[vsl]

From experience: when tired, glancing down while driving is hard, while glancing sideways (at nav) is fine.