Recently there was a discussion on calibrating the Anova Precision Cooker. Calibration is comparing a device to a standard and adjusting the device so that it matches the standard. In actual practice this would be done over the operating temperature range of the device you are calibrating. One requirement is that the standard must be more accurate than device being calibrated. If it isn't you could end up further off than you started. I think the Anova would require labratory grade equipment to be calibrated and it is surely outsicde the home cooks capabilities.
The Anova is far and away the most accurate measuring system for temperature in any of our kitchens. My suggestion is to use the Anova as a standard and use a stable water bath to test your thermometers. At the low end an ice bath will get you close to freezing. Very few home thermometers can be callibrated but it is good to know how far off you are. the thermometers that use a moving needle to display tempreature are notoriously inaccurate. BBQ thermometers may be off by many degrees and your food will know the difference.