We usually hit really close with the auto level on our Challenger, but I will use the bathroom door as a level just to double check and it works great. Open the the door about half way, if it swings closed or open, you're off a bit, correct as necessary. Also have a level app on my phone which will get really close as well. Just beware your phone case may affect your readings.
I usually end up within about .1 or .2 degrees of level, no problems.