What is the negative CPU value in Speedfan?

It varies in the low 40's usually.

I have an Arctic Cooling Freezer 7 Pro CPU cooler (which is mounted correctly, it doesn't budge and was cleaned before reapplying thermal paste when upgrading from E6600 to Q6700), and used MX-2 Arctic Cooling thermal compound and am getting those temps at idle. I opened the side panel of my case and temps went down to the low-mid 40's. I was looking at this cooler http://www.newegg.com/Product/Prod [...] 6835118046
as a replacement since this one doesn't seem to be doing very well cooling a Q6700.

I was also thinking about replacing the stock rear fan with a high flow model.

But mainly, why is that CPU value negative? Is it just refering to the spread remaining from the Tj. max value or something different?

Thank you for any info.