I'm trying to use a FRDM-KL26Z as data reference for my own sensor (based on a FXOS8700 as well). I do need the vector magnitude of the acceleration. To get the data I use the Freescale Vibration Monitoring software. In that software there is a |XYZ| Modulus which according to the help file is giving the "magnitude of the combined channels". Why does the software still show negative values? Does anyone know based on which formula the values are computed?