A regular pressure cooker has a pressure release valve which lets steam out if the pressure inside is 15 PSI above atmospheric pressure.
If you're at sea level, this results in faster cooking, than you'd have in a normal pot at sea level.
If you're on a mountain top, this results in cooking at
the same speed as you'd get, cooking in an open pot at sea level.
What if you're a mountain climber, and want to cook food at the same speed as if you were at sea level, using a pressure cooker?
Enter the GoldCo brand Absolute Pressure Cooker.
Instead of determing when to release steam, by measuring the difference between the internal pressure and the surrounding atmosphere, it measures the pressure difference between the internal pressure, and a pre-calibrated sealed air reservoir.