I am using the ferroelec­tric test module (Premier II, Radiant Technologies, Inc.) integrated with a high-voltage amplifier (TREK 609B). I have measured the P-E loops of the PZT sample using Vision software. In the vision software, the P-E hysteresis loops appear to be symmetrical and centered but when I plot it on Origin software using the exported an Excel file, it is shifted. In an Excel file, it shows negative values even when I have selected the monopolar profile. Why I am seeing this issue and how can I correct it? Thank you.