Accelerometer measures the static gravity field

Acceleration of 9.8m/s = 1g

Changing the tilt (along the sensitive axis) changes acceleration vector

q = arcsin[(V(out)-V(zero g))/ (1g x Scale factor(V/g))]

Important Specifications

Since gravity is static (DC), absolute accuracy is important

Drift of zero g bias affects how accurately you can measure tilt

Low hysteresis & repeatability are important

High resolution is important as 1 degree of tilt is 17mg

Noise level is the chief determinant of resolution