Speedfan Temperature Accuracy?

I have downloaded Speedfan 4.37 onto my computer. I was wondering how accurate the temperature readings are on it. I was getting 60*C for my video card at idle, 75*C+ at load. I installed a liquid cooling unit on the card and it is now running at 44*C at idle and 52* at load. That is a nice drop as long as the readings are accurate and yes, this is the "Inferno" of a video card..aka BFG 8800 GTX OC, lol. This thing has ran hot ever since I bought it and already fried two because they run at such high temperatures.

Also, on my other temps at idle here is what I get:

System: -10*C
CPU: 29*C
AUX: 32*C
HD0: 36*C
Core 0: 33*C
Core 1: 26*C
Core 2: 24*C
Core 3: 30*C
Core: 44*C

I know the Core 0, 1, 2, 3 are for the CPU core temps and the Core is for the video card. I am assuming HD0 is the hard drive and CPU is the average CPU temperature. What are System and AUX for? Do these readings look normal?

Thanks in advance.