Yeah, redrob, I think we are saying the same thing - we can eliminate some variables from the equation by using consistent calibration techniques, but there are other variables (particularly things like the movie being watched and the individual's preferences) that will insure that we don't all get the same answer.

As for the question of the decibel scale, it gets complex pretty quickly. The scale is actually logarithmic, which makes acoustical analysis all the more interesting, but for the sake of this discussion the answer is yes - if I calibrate at 0 and you calibrate at -10, then my -10 and your -20 would be equivalent (all we've done is move the "zero" point). This all reminds me - I need to go through some recent seminar notes and update my technique for HVAC acoustical analysis. Maybe in a couple weeks...