This is a saved historical sample of the IOM's onboard memory (DIMM) temperature at a specific past collection interval, the historical counterpart to the live dimmTemp field. It lets an admin trace how memory temperature evolved leading up to a past event, such as a management-plane hang on that specific IOM. For example, a rising trend across historical dimmTemp entries in the hours before a card's management processor became unresponsive would support memory overheating as a contributing factor.