Thermal Sensor Reading Off? PCChips m830

Does anyone know how off this sensor is - if its off at all? Its running an AMD Duron 700mhz 100mhzfsb - 1.6143vcore - about 42C - 43C idle in the bios. I know that cant be right...its a stock heatsink with an 80mm 2500rpm fan on top of it. It at least gets 37 - 39C idle...could the sensor be off by any?

When in the bios, its not at idle...Thats prob. the diff. your seeing...