I have a digital thermometer that I use to measure outdoor temp. The probe wiring broke down due to being outside for many years. I have no way to ohm out the probe to determine its resistance value. I tried another probe and measured it at around 30k ohms at 75'F. It works, but my reading is off by about 100'F I am fortunate that the unit has a trim pot that I can fine tune it, but I don't know how to determine what resistor I will need to get my temp reading down 100'F. I'm sure this is probably easy to figure out, but I don't know where to start. Help please.