With a Sinar, you really want a Sinar glass. There are dotted lines indicating the location of the swing and tilt axis, and even on a Sinar F, the dotted lines are necessary for using the swing/tilt calculator.

So imagine you've got an 8x10" back on a Sinar P. The swing and tilt axes are around 1.5 inches (from memory, without taking the camera out of the case) from the bottom and right edges of the groundglass, as indicated by the dotted lines. Try tilting and swinging the rear standard, and you'll see about where the axes are. Now imagine you've got a 4x5" reducing back. The swing and tilt axes will be outside the 4x5" frame, so you can't focus with a loupe on the axis. You can make do, of course, but the main attraction of asymmetric tilts and swings on a Sinar P is this feature, which makes it very easy to find the best tilt and swing angles.