Difference in harmonic vibrations while in use?

Device may be sensitive to differences in vibrations from the mounts being used. Try just carrying your device in a pocket, see what you get out of it.

Possible too that the unit you bought is defective. You'll need something else capable of measuring changes in elevation to bring you numbers you then can compare to those you're getting from the Karoo. Googling <karoo 2 elevation wrong> brings up lots of potential causes....