Quote Originally Posted by gma
When you are making the exposure you see the whole square and not a cropped rectangular image.
There is a way around this: Opaque document-tape in the corners of the groundglass. The screen in the Hassi is covered with sheets of glass, bottom and top. Appropriate markings are easy to apply and remove.

BTW.: The outside-lines on the grid-screen approximate 4.5x6 vertically and horizontally.