Measuring the air temperature of a refrigerator or freezer accurately is very very very difficult to do. To calibrate a thermometer inside a refrigerator it must be placed inside a container with a large thermal mass and shielded from any moving air. We calibrate inside a large heavy metal box. This is the only way to get a steady fairly accurate measurement. The air inside refrigerators and freezers is always moving and there could be as much as several degrees difference just one or two inches apart. Even thermometers placed side by side could read differently because of the many factors (thermal mass of the thermometers, built in temperature buffering, position. etc...). So if you have a thermometer calibrated by a metrologist it will be accurate to the specified accuracy but that won't necessarily mean that it will measure the actualy temperature of the unitit is placed in. Comparing the temperature accurately of one refrigerator/freezer to another is impossible. We sell thermistors, digital sensors and thermocouples which have an accuracies of between 1.0° and 0.1°C. When we calibrate them we must take extreme measures that you would probably never be able to duplicate in your blood bank. My suggestion is to take the accuracy stated by the manufacurer and accept it. If you need the thermometers calibrated your best bet is to get some else to do it. The accuracy of the thermocouples built into the refrigerators and freezers are probably good enougy but even the manufacuter is reluctant to tell you how accurate their thermocouple is becuase of all of the many factors inherent in any individual refrigerator/freezer. Hope this helps
