RTD Temp offset in logix 5000

We replaced a RTD probe and the new one is consistently 18 degrees too high. There is currently a MOV instruction moving it from local:5.I.ch3data to HMI real[30]. My question is, is there some math going on to get my value at local:5.... and can I modify that or should i make this a cpt instruction, sub, or something else. I tried to use a cpt instruction but I couldnt make it accept my expression I guess my constant of 18 would have to come from a file somewhere not really sure as I am mostly self taught I can read and mostly follow a program to help troubleshoot a machine but at my facility I have turned into the plc goto wizard, which i'm trying to leverage into them sending me to classes but thats another subject, maybe I should stop figuring out how to make things work. lol

You did not mention what plc you are using, but with compactlogix 1769-IR6I you can use sensor offset in configuration and forget about any additional instruction, same with 1756-IR6.

Check your RTD temperatue connections for corrosion and tightness,
bcause it would only take an additional 3.9 ohms to
give you 18 deg F or 10 deg C off with a PT100 RTD