Ah, OK. Thanks again. (In retrospect, the amplitude question should have been obvious once you told me the 50 ohm terminator will be engaged. It wants a 10V signal, and if that were center-peak that would exceed the maximum power rating of the terminator.)
One more question, this time purely out of curiosity - hopefully you or someone else here can guess at this, because I'm stumped. I've started the routine, and at one step, it performed a sort of automatic adjustment of the vertical cursor alignment. Now, as far as I can tell, the MPU has no way of knowing what actually appears on the screen, and some other steps of the adjustment appear to confirm this. It blanked the screen and played a little dot around, and I swear to god it looked like it was performing a slightly modified binary search looking for the graticule lines. Unlike the other steps, at no point did it require me to move the dot for it onto a specific point. Does anyone know what it's doing here?