This is a saved historical sample of the ambient air temperature, in Celsius, recorded near this IOM at a specific past collection interval, rather than the card's current live reading. Comparing a run of these historical entries lets an admin see whether ambient temperature has been trending upward over hours or days, something a single live snapshot cannot show. For example, a series of historical ambientTemp entries climbing steadily from 28 to 40 over several hours would reveal a gradual cooling degradation that checking only the live row would miss.