Barometric pressure correction doesn't make much difference on Dyno Dynamics software and the greatest influence on dyno readings is ambient temperature. Low barometric pressure makes an engine run rich and that'll show a lower dyno reading with carby engines or EFI engines that have ineffective barometric pressure correction calibrations at different geographical locations.
If you tune an engine in SA at an average atmospheric pressure of 101kpa for example and take the car to Bathurst where the average is around 93kpa, the engine will run rich and effectively suffer a power loss. Phillip Island has a barometric pressure shift through a lap with an engine typically running leaner down the front straight. It's the worst circuit in Australia for blowing engines on the lean side from the barometric pressure shift.
Yea but it's not just barometric pressure.
It's also absloute water volume in the air which is not relative humidity.
As water volume changes the power will change, as with air fuel and compression.
It's not ad simple as you make out, and no I don't know either, but when multiple engineers have to explain something in a team it's complex.
Superflow is the leader in dynos and they have adjustablity for correction factors, which are not spot on but better than fixed numbers.
By the way I would buy a Mainline over a DD any day.