iOS 7 Beta 6 Compass Level is strange

[Wikwoo]

On iOS 7 beta 6 on my iPhone 5, the level in the compass app is really weird, sometimes it will show -1 even though the surface is in fact level, confirmed by my iPhone 4 (also on beta 6) and a physical level. Sometimes it will show that the surface is level, but sometimes if I put it back on there it'll show -1 again.
I noticed it works a lot better without my case on, which is just a cheap rubber case I got free with the phone. I don't like putting it down without the case on because it gets the back all dirty and I'm paranoid about back scratches (I don't want another metal back iPod touch again *shudder*) and sometimes if I tilt it until it is at 0 degrees and set it back down it will stay at 0, but this doesn't always work. (Sometimes it will never go to 0 ) And on a somewhat unrelated note: What is that second mode in the level that's red and turns off after you tap on the level? Does it have any function besides a different look?

 

[MinEderPlayz]

Might the case be slightly out of shape? It seems like it has a little slope on the back and the iPhone doesn't lay on the table very flat.

 

[Virginaustralia]

I dont need to care about that stuff, i have an ipod touch loljokes the guy above me is probably right

 

[Wikwoo]

I forgot to mention that even with the case off it still doesn't work half of the time.

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Ok, so I found out what "red mode" does, it sets the current angle as the new 0, which is handy for when the thing won't go past -1, and for some reason even tilting it around I can't get it to 0, it always goes to -2 or -3 and goes around the middle.