how are they reading boost pressure? MAP sensor of some kind??
What happens is (on sealed liquid filled boost gauges) is that the internal pressure can make the gauge read incorrect, and you need to zero the gauge out, in the altitude before riding.
Boost pressure and MAP pressure are two diffrent things, boost is pressure above whatever atmospheric pressure is, MAP (manifold absolute pressure) is basically 14.7#'s (ideal atmospheric pressure or whatever the calibration is) plus boost in a sense is the same in design but you dont get 14.7lbs at 10K feet, MAP is calibrated to a set point. 02 or AFR gauges are the same as far as calibratiting them in diffrent altitudes.
sorry if this sounds confusing.