Oftentimes when your device temperature and an external thermometer source does not match, it is due to heavy evaporation and inadequate waiting periods.
Simply cover your tank with foil and wait for about 15 minutes for temperature equilibration. Once the water temperature is stable, complete a second read.
Please keep in mind the Anova Precision Cooker is calibrated to a scientific platinum primary standard which is far more accurate than consumer-grade thermometers. Candy thermometers and meat sensors are not accurate enough to warrant a calibration. We recommend a Thermapen or higher grade thermometers.
If you want your system to match your personal thermometer:
Use the calibration function within the Anova app to calibrate your device accordingly. Calibration directions can be found here.