There are a number of different temperature points which can be measured. Each IA core has its own thermal diode as well as the PCIe controller, memory controller, integrated graphics and cache. These temperatures will fluctuate very rapidly as they are the source of the heat itself. There is also a thermal diode on the package which shows a more aggregate measurement as well as additional thermometers that the motherboard manufacturer may install. HWInfo will monitor as many of these as it can and label them as such. The system firmware often only measures one or two and doesn't tell you what it is measuring or how it is measuring it.