Are Inclinometers/Angle Gauge's independent of gravity
Inclinometer axes in general are sensitive to changes in angle when the axes are both perpendicular to the gravity vector (near zero.)  As you rotate the axis from parallel to the earth's surface, the response from an axis is proportional to the sine of the angle.  The difference between the sine of 0 degrees and 1 degree is .0175; between 89 degrees and 90 degrees the difference is .00015.  So an inclinometer is more than 100 times more sensitive when measuring near its zero output when compared to trying to make a direct measurement of the gravity vector.  This is the reason that inclinometers are generally two axis and not designed to measure high angles.

Some higher-end inclinometers work by means of a mass on a beam magnetically centered by providing a current through a coil; the coil current required to keep it centered provides the measurement.  Less expensive inclinometers can have cantilevered beams and use capacitance to measure beam deflection.  I'm sure there are other techniques.  They all work using gravity.