Im not sure if this is the right place for this but I dont know what the bios means by the chassis temp. this is found when changing the speeds of the chassis fans. the lower temp is fixed at 40'C and the default higher temp is 70'C.
I have the ASUS m5a97 pro mother board if that has any relevance
Chassis temp is the temp of the MB. There is a sensor (usually near the chip set) that detects the temp. I'm not sure what your question is about, though. You may be talking about the SYS FAN speed settings in BIOS. Some boards allow you to control the speed of the fan(s) according to the temp of the sensor. If in doubt, leave it at default.