This is a simple 160mm X 160mm X .2mm solid single layer square for testing the heck out of my level.

Do you think you could have made it bigger? Sure.
Is it overkill? Probably.
Can it clean my magnetic bad to an awesome shine? No. But it can clear old print residue from it and bring it back to it's lack of luster.

This prints a big 'ol square to set in your level. I was using a square level test that printed several concentric squares, but I had issues with it. It started in the middle and wasn't really helpful until the 3rd square when you could flick the filament and check your adhesion. Then you only had a few squares to try and rush your way though to get it right before you had to run it again. This prints the fist wall squares from the outside in which works better for me. It then starts diagonal lines from the left rear corner working across on the diagonal to the front right corner. As it works it's way across you can see if your having bed warping and the like if the diagonals fail to adhere or the nozzle starts to dig in to your lines. It's a pain in the butt, it takes around an hour on standard settings, and it uses a bit of plastic; but once it runs right I know my bed is good to go for a while.