Atmospheric pressure and boost.
I have had a few high elevation customers wonder why their cars aren't making as much power as they should or aren't performing as well as other cars similar to theirs. The reason is air pressure is thinner the higher you go in altitude or DA(density altitude--a separate discussion)--which is basically a combination of temperature, elevation, and humidity and the only way to find your true elevation as it affects performance.
At sea level, the air pressure is 1.0 bar or 14.5psi. That's the air you breath and what your engine makes at 0 vacuum/0 boost. On your logger, if you see boost banks 1/2 making 14.5 PSI, that's 0 boost and 0 vacuum. Anything below that is engine vacuum and anything above that is boost.
When you have someone like Tyler whos base atmospheric pressure is 0.627 bar(9psi) because he lives up near Heaven at 6400ft above sea level, the performance of the car is going to be massively reduced due to the much thinner air. On his logger, if he sees Boost banks 1/2 making 14.5psi, because his atmospheric air pressure is only 9psi, he's actually IN boost 5.5psi. If he sees 9psi on boost banks 1/2 his car is making no boost and no vacuum and anything under 9psi is vacuum.
Here is where it starts to suck. If I target 18psi of boost on his car, the ecu will purposely re-calculate and target 5.5psi of boost less and consider 12.5psi of boost as perfect and give a 0 for boost error. The reason for this is because THE STOCK turbos can only spin so high before they come apart. So, (this isn't exact, just an example) at sea level or 1.0 bar atmospheric pressure, the turbos spinning at 250,000 rpms at xxxx engine rpm will produce 20psi of boost at the engine. At an elevation of 6,000 ft above sea leavel or 0.627 bar atmospheric pressure, those same turbos at 250,000 rpms at that exact engine rpm will only make 14.5psi of boost at the engine because they have to make up for that missing 5.5psi due to the air being that much thinner.
Less air means less fuel. Less air and fuel means smaller bang. Smaller bang means less hp. So, a car on stock turbos at that elevation will NEVER run anywhere near as fast as a car at sea level. His car will be much slower at any given turbo speed than it would at sea-level. In fact, if he draggy'd the car at 6400 ft above sea level and did NOTHING to the car and drove down the mountains to sea level and re-draggy'd, not only would the car FEEL much faster, but the draggy numbers would drop dramatically as the power levels would go up simply due to the amount of air the turbos are able to shove into the engine.
Lastly, You can solve this by putting aftermarket turbos on the car capable of spinning much faster(flowing more air) to make up for the boost deficit and at that point turn off the elevation calculation in the software and run actual boost measured at elevation and match power levels.