Each system is calibrated by the manufacturer and may not match exactly. If the temperature readings are within 3 degrees this is within the specification.
The temperature from one device to another is difficult to determine. The location of the thermostat is very important to the temperature that you are reading at any point in time. The important thing to remember is that you should develop a comfort area and the appliance will keep you at your comfort level rather than the exact temperature read out.
