Well, do you want just gravity, or do you want all acceleration?
With acceleration:
X = -Touch.AccelerationXWithG
Y = Touch.AccelerationYWithG
Just gravity:
X = -(Touch.AccelerationXWithG - Touch.AccelerationX)
Y = Touch.AccelerationYWithG - Touch.AccelerationY
Then:
Angle = angle(0, 0, X, Y)
Oh my god! Thank you so much!
I've been trying to switch to Unity in order to get this to work, but you saved me a lot of hassle!