Playing with the application some more, I was able to find a number of air pressure measures. I started a log file, took a drive, and goosed the engine a few times to see how it might work or be estimating boost. The log viewer is pretty cool because you can play it back after your run and watch the data from someplace other than the driver's seat (better than watching all this while you are driving), and it also records min, max, and averages for each value that you configure into the log. Test run max values are shows below:
boost presure estimation (by DashCommand) - 25.8 psi
Ford Engine measured boost at throttle inlet pressure sensor - 30.5 psi at max recorded value (14.1 psi at idle)
Ford Engine manifold absolute pressures sensor - 13.9 - This appears to be a a sensor that just sees atmospheric pressure as a reference and did not change during my run
Ford Engine intake manifold absolute pressure - 52.6 "Hg. At idle this was 3.2" Hg (meaning that the engine makes a fair amount vacuum when not in boost)
I'm guessing that boost should be the difference of either the throttle inlet, or intake manifold pressures and atmospheric pressure. Converting all of the measurements to psi and doing the calculations:
throttle inlet difference = 16.6 psi
intake manifold difference = 11.9 psi
Based on Nasty Wendy's comment the intake manifold is probably the correct measure?
The "estimated boost" by DashCommand appears to just convert the intake manifold pressure to psi. If you convert my max intake manifold pressure (52.6 "Hg) you get 25.8 psi which matches the max calculated boost that I had in my log. The program probably assumes that this is a gauge measurement instead of absolute measurement (which includes the 13.9 psi of atmospheric pressure). So long story short, it looks like you need to take take 14 psi off of the DashCommand value and you have actual boost. It would be nice if they calculated it the right way. I filled out their feedback survey and made this suggestion.
Fun program. Haven't been able to rationalize a legitimate use for it yet but I enjoy it. Thinking about setting up a screen to watch boost, instant mpg, knock control spark retard, and transmission temp for towing. The knock retard might tell me the difference between premium and regular gasoline when I tow something heavy.