Giant bubble levels

Something to think about when using a bigger level that has the metal ball as a reference instead of a "bubble": if your trailer is off level and your trying to determine which is the low side, a bubble on a bubble level will go off to the high side but on the metal ball type the ball will of course roll to the low side.
I have both types of levels on my rig and I was in a bit of a hurry one day trying to determine how many boards to put under the wheels and I kept screwing up by reading my metal ball level wrong!
I say again... I was in a bit of a hurry....I know that reading a level is pretty basic...