For tCase, For def:
quote: Tcase: Technically this refers to the temperature that you can measure using a thermocouple embedded in the centre of the heat spreader, but this is only done in the factory by Intel or by users willing to drill their heat spreaders open to insert a thermocouple. Therefore Intel provided a diode between and below the cores with a reading calibrated by the BIOS which can be used instead. This reading can vary greatly when the BIOS version is changed, but will not necessarily change if the BIOS calibrations were not altered between versions.
Software supplied by motherboard manufacturers typically reads only this sensor, not the DTS. It is often labelled “CPU.” SpeedFan usually labels this as “CPU” as well.
Much more in link about Tjunction ect. very good read.
TJMax which is the safe maximum operating core temperature for the CPU. As your CPU heats up, your Distance to TJMax will decrease. If it reaches zero, your processor will start to thermal throttle or slow down
You do not change UNLESS you know it is incorrect, And I believe it is.
While 73 is on the high side, it is OK (Should not go above 80->85 C) Myself I like 60 or Below.
It does not sound like you have OCed this yet - And I"ll bet you have the stock HSF installed. Note: the intel hsf is at the BOTTOM of the list for performance - politely - it sucks. get an 3rd party HSF, about $30-$40. That said have you verified that all 4 push pins are seated correctly and is the thermo paste properly apllied - most here prefer AS5. It takes VERY little, about the size of a grain of rice.
HOPE THIS helps