If the controller can't be calibrated, test the thermometer in boiling water and determine what temp it should boil at for your elevation and the baro pressure at that time, then either make note or adjust the thermometer if it can be.
Even if no adjustments are possible, you just need to determine what you want the thermometer to read for the temp desired.
I like to run my bottler at 187+/-1, it seems to be that close. Yours may be a wider spread, just be certain it is never below 180 nor over 190F and it should be fine.