TrevorUAH

We use the product by BD (the SP100). They actually sell a calibration software for their unit, so the first thing I would check into is if the company that provides your buttons can do the same. If they don't, the procedure you have described is very close to how the BD system works. You basically plug the cable into the logger, and enter the temperature the reference device is displaying (after a 2 hour stabilization). This is only a single point calibration, but is the manufactureres method. Only recommendations I can provide is to maybe wait longer than just a few minutes to make sure everything is stable, and try to avoid a "drafty' area to do this in (you especially don't want to have your PC fan blowing right on the area of either device when doing the room temperature check - when doing the cold check, use a lower drawer in the fridge, or just be sure the inside fan hasn't clicked in - this one can be tricky), second, double check that the loggers internal clock is syncronized with the clock that you are recording the reference devices reading time from (that way your comaprisions are of readings that are as close to the same time as possible). Hope that helps.

That section in the AABB TM regarding the 2 is intended as a check on the thermometers themselves, not the storage cabinet. Each thermometer should have an accuracy tolerance of +/- 1 oC. If the difference between the two is greater than 2 degrees, then you probably have a calibration issue. Later on in that section it does talk about multiple thermometers in larger storage units, and as mentioned the only thing that matters is that they are all within proper range, not how far apart they are. Having said that, we just buy all NIST traceable thermometers for all our storage units. Doesn't cost much more, and it remove alot of issues around calibration! I know the standards state that the lower limit is 1 oC, and we adhere to that very stricktly, but for interest sake, one of the researchers we work with has done extensive work in the area of cryopreservation of various products, and they have demonstarted quite well that packed cells are not adveresly affected (aka "frozen" ) until around the -4 oC mark.