Cooler thermometer calibration

Hi There,

We have two big coolers in our plant, we have two probes in the each cooler. 

Do we have to have a calibration certificate for the thermometers in the coolers or can we use freezing point method to calibrate it on our own and record it, just curious if that would cause a problem for 3rd party audits?

Thanks, 

You could have 1 calibrated by 3rd party and annually verify the other one HOWEVER, you need to have a certified thermometer you can use to verify the accuracy against, so unless you can remove the one from the freezer, you still need to pay annually for a 2nd thermometer to be calibrated and certified