I mounted to probe in the log manifold just to the front of the number 8 cylinder.
It was 64 degrees outside, that's why it says 64. Hadn't started the truck yet for the day.
For everybody's information, the 3 bar map pressure sensor from Auberin's that is bundled with the boost gauge is an absolute pressure sensor. You can get it to read manifold boost by setting the offset, but then it reads what the barometric pressure is when the engine isn't running. That's why mine says -1.5 (I'm at ~2500 ft.). On the other hand, it could be a quick way to reference just how much thinner the air is, say, when you are going over that pass than it is where you normally run.
I kind of wish I had ordered the 205G, which would read relative pressure. Too bad it's $22 more. In the end, it's not a big deal, just something to think about.