How to calibrate Polder instant read thermometer?
You can download the manual for your particular model on the polder website.

The instructions for the model 574 (not sure if that's yours) are:


  Calibration function: Put the probe into iced water (32 F); wait until the reading value stabilizes. ␣ If the value reads between 23 to 41 F (-5  to 5 C), press the “CAL” key for 2 seconds. “CAL” will appear on the display for 2 seconds: the unit will then be calibrated automatically and return to its normal state and display 32 F.


You can always give them a call too.