KSP | Haul Mk16 Parachute into flight above Kerbin
Minimum pressure is the pressure the chutes first deploy, as a fraction of the air pressure at Kerbin’s sea level. So if you have that set to 0.5 and a barometer on your ship, you’ll see that it deploys at ~50 kilopascals. The altitude setting is the height above ground the chute fully opens.