How the correction works
The source chart states its own rule: a 12 psi cooker needs about 20% longer than a 15 psi one. That anchor gives a linear factor of 1 + (15 − psi) × 0.0667, applied to both ends of every range and rounded to the nearest half minute.
Foods marked low are cooked on the low setting, which the chart pegs at roughly 8 psi; those are corrected against that datum instead. If your cooker has no low setting, use high pressure and check well before the stated time.
Weight only moves the clock for cuts cooked as one solid mass — a joint, a whole bird, a meatloaf. The chart's own two whole-chicken bands (1150 g at 12–18 min, 1600 g at 18–25) imply time scales with weight to the power 1.09, so it scales linearly from each cut's stated reference. For everything else, thickness sets the time: twice the stew cubes is the same time at pressure, it just takes longer to get there.
None of these times include the minutes spent coming up to pressure — typically 5–15 depending on how full the pot is — or the release. The timer starts when the pot reaches pressure.
Source & pressures
Time tables transcribed from the fastcooking.ca cooking-time charts (via the Internet Archive — the original pages are gone). Operating pressures come from each manufacturer's published specifications.
Approximate times for home cooking, not a food-safety authority. Always follow the manual that came with your cooker — minimum liquid volumes and maximum fill lines differ between models and matter more than any number here.