C
Ah... didn't know you have 13 of these. That makes the economics different.
Whatever accuracy you feel you need the instruments in the freezer rooms, then you want a standard that is sufficiently more accurate than those. So in general, if you are going to have them at +/-°F, then your standard needs to be 1°F; and, it should be reliable and repeatable.
So I would invest a couple of hundred in a decent instrument. Set it for one year interval. Since these are freezers, I would get an extension long enough for the probe, where the meter sat outside the chamber. I would perform a once a month verification on the rooms/thermometers, and log on a sheet you keep by the rooms.
Whatever accuracy you feel you need the instruments in the freezer rooms, then you want a standard that is sufficiently more accurate than those. So in general, if you are going to have them at +/-°F, then your standard needs to be 1°F; and, it should be reliable and repeatable.
So I would invest a couple of hundred in a decent instrument. Set it for one year interval. Since these are freezers, I would get an extension long enough for the probe, where the meter sat outside the chamber. I would perform a once a month verification on the rooms/thermometers, and log on a sheet you keep by the rooms.
According to the manufacturer, usually this is the kind used by others who do stuff like we do.
The good thing about this is that, the acclaimation time is within seconds. That means if I bring it in one room it detects/stablilize and will give the accurate reading within seconds.