Does anyone know how to calibrate a Polder 362-90?

Good morning, gang. I have my GOSM fired up and loaded with 3 packer cut briskets and 2 butts. I got out my thermometers and noticed that one of my Polder 362-90 units was reading 17 degrees cooler than the others. I tried switching probes to see if that was the issue and it is not. The same unit still reads low. Does anyone know how to calibrate these units?

Thanks, Shawn