Try reading the section on Calibration in the documentation for some background info:
http://www.techpowerup.com/realtemp/docs.php

The best way to calibrate is to drop your processor down to a fixed value like 6x266MHz for 65nm or 6x333MHz for 45nm and then drop the core voltage to about 1.10 volts. Open your case and let us know a few details like what CPU you're using, what your air temperature is or water temperature if you are water cooled. A typical Quad will report temperatures about 6C above your air or water temperature during this test. Make sure your CPU is as idle as possible and that it doesn't have any background processes running that will effect your results. This is not an exact science but should get you in the ball park.

By the looks of things, I'm going to guess that you have a 45nm Quad and core0 and core1 might be very close to the sticking point. Intel says these sensors can "bottom out" at any temperature below 50C so you have to be careful when trying to calibrate. Sticking sensors can not be properly calibrated with my approach but I have a plan B if that happens. 45nm sensors can be a little on the wild and crazy side.

I was helping someone yesterday running a dual boot system with Windows 2000 and Windows XP. His load temps were the same but his idle temps were about 10C lower in XP than in 2000. I think it's because Windows 2000 wasn't letting his Core 2 Duo go into C1 at idle so it was running hotter. Anyone else heard of this before?