Hi folks.
Just in case you did not saw the tutorial where this was shown, you can use a double inference from two adjacent sides of a rectangle (or square) to get its center. The procedure is as follow:
1 - Find the inference from the midpoint of one side. Wait for the pop-up to appears.
2 - Immediately find the inference from one of the midpoint of one of the adjacent sides. Wait for the pop-up.
3 - Move roughly where the center should be. You shall see inference lines to both choosen midpoints. This is the center you want.
Just ideas.