Most inclination sensors available on the market today feature a 3-axis (x/y/z) MEMS accelerometer.
Depending on the sensor type, the final factory calibration determines which measurement axes and also which rotation orientation are used for the respective article. This means that almost any type can be generated from a 3D measuring cell.
Inclination sensors can be mounted horizontally or vertically.
The following pictures illustrate the sense of orientation and rotation as a function of the mounting position.
If the sensor is mounted horizontally, it can map a rotation around its x- or y-axis:
If the sensor is mounted vertically, only a rotation around the z-axis makes sense for a 1-axis sensor:
If a 2-axis sensor is mounted horizontally, it can map a rotation around its x- AND y-axis:
In vertical position, the 2-axis sensor can also output x- AND y-angles: