I have a Graphic View II which I use the mainly shoot flat art (oil paintings).
Is there a precise way to square up the camera. Right now I tweak it visually to get the image straight. Thanks

If I'm setting up for something big I will measure from the outside of the copy area to a central point onthe camera to make sure its even side to side and top to bottom.

then I place a front surface mirror inthe center of the copy area. By focusing on the reflection I've doubled the potiential error. When the reflection of the shutter is round and centered. I'm square.

there is/was a company called Zig Align that made a mirror with a small hole in it. This went on a lens board and you could look through the hole and the multiple reflections between the to two mirrors. When you got the cascading reflections straight you were perfectly square, as long as the mirror was flat to the wall. ( They also made one using a laser somehow)

Another way to use make up a grid and use that as a target. It's easier to see if any of the lines are converging on a black and white grid as opposed to say a gold leaf frame of a painting.