Once it’s setup, you shouldn’t need to adjust it further…depending on what you’re doing with it. If you’re constantly switching it from a CNC to a printer, you may need to.
The problem with pipe like this, is it could be bowed in the center. Measure from outside corner, to outside corner, if they are the same, your frame is square. Like I said though, in the center, one side could be bowing in slightly, which will cause issues all over.