Bias shift in ShapeArray™ data is a known behaviour that can sometimes occur with the legacy MEMS accelerometers that were used in the construction of our Model 3 and older SAAF and Model 1 SAAX products. The nature of these MEMS accelerometers is that the zero reading can sometimes shift instantaneously which causes small jumps (typically less than 1 mm) in the reported data.
To account for this behaviour, Measurand's software has a Bias Shift adjustment (formerly known as eXYZ correction) that can be applied to the data at conversion time. The software looks for discrete jumps in the raw data counts from a single axis only (x, y, or z) that has no corresponding changes in the adjacent segments and corrects for the zero reading. The bias shift adjustment is applied automatically to vertically installed model 3 SAAF data at the time of conversion and is not typically used in other applications such as horizontally installed SAAX unless a need to do so is explicitly observed.