Make sure the post is 'square' to the floor. [=make sure that there is a right angle where the post and the floor meet]
I'll go on the trip if I can 'square it with' my parents. [=if my parents will agree to let me go]
Here's the rest of the money. Now we're 'square'. [=now we don't owe each other anything]
(..) For instance, you can accept that your father was a pirate and a good man or you can't. Pirate is in your blood, so you'll have to square with that someday. Now, me, for example. I can let you drown. But I can't bring this ship into Tortuga (..)2003 Pirates of the Caribbean: The Curse of the Black Pearl
(..) Now if you'll be very kind. Easy on the goods, darling. You're despicable. Sticks and stones, love. I saved your life. You save mine. We're square. Gentlemen, milady, you will always remember this as the day that you almost caught Captain Jack Sparrow. Whoa! (..)2003 Pirates of the Caribbean: The Curse of the Black Pearl