My tank is 6 feet long, and from one end to the other it's out almost an inch. Been like that for around 2 years....no problem!
I'm on the 5th floor of a concrete building...for a while I had a 110 on another wall perpendicular to my 130. Good thing the building manager didn't see them both! They were a little worried when I had my 55gal before I upgraded to the current 130!
I think if it's out 1cm, you're doing pretty good!
