Quote Originally Posted by dpurdy View Post
If the image on a ground glass were actually upside down and backwards, you could hold a mirror under the ground glass angled for you to see and it would be right side up and oriented correctly.
Nope. You'd have to flip it twice. Once vertically, once horizontally. Which is why there are pentaprisms in DSLRs. They have to flip it twice because the image is both upside down and backwards.

This is clearly beyond my ability to explain to you. Such is life; I'm not a teacher. Find someone near who uses a view camera and they can give you a demonstration maybe. Or a local physics teacher can show you maybe.

BTW, if you are standing on your head looking at the ground glass, it's you who have flipped twice. Once horizontally (which puts you on your head looking away from the ground glass) and once vertically (flips you 180 degrees so you are looking at the ground glass).