Pool walls out of square

[Manslick]

Thought of a way to check radius corners for square.

Look at the attachment. You need some blocking at least as wide as the radius.
Cut two square pieces of plywood. You’ll probably need an extra pair of hands to hold them agains the wall. Set the blocking as shown and use the framing square to see how it looks.

They may even make offset squares for just such a situation.

Just an idea.