I'm getting better at cutting the short rips for tenons. I clamp the piece vertically, and line it up in the vise with the square, then do the two long rips. They're sometimes annoying, and I'm not very good at going straight still. But then, without moving the piece, I turn 90° and cut the short rips, without marking anything or doing anything other than a) getting my eye over the top of the saw and b) looking down below the vise at where the other end of the piece is — that latter is a new trick for me, and it's amazing how much easier it is to get aligned that way. Then, it's just a matter of cutting down, quite quickly. It works pretty well and repeatably, although I'm still not very good at stopping at the right point: I keep either going too far (rarely) or (more commonly) not far enough, so when it comes to cutting the cheeks off I have to saw sideways a bit.
I'll do another eight, and see how things improve.
Incidentally, the Woodworking vises category on Commons needs more photos! https://commons.wikimedia.org/wiki/Category:Woodworking_vises