VPM Program Settings
Units and Constants
The calculations were done in pressure units of "Atmospheres," with 1 atm ~ 1 bar~ 105 Pascals. So when you see a "33" in the code, this is a conversion of units: 1 atm = 33 feet of salt water. Note: 33 feet of saltwater = 34 feet of fresh water. 3.3 feet of anything = 1 meter.
The partial pressures of water vapor and carbon dioxide, set as ppH2OCO2 = 102 / 760 in SUB DIVEDATA, are subtracted from ambient pressure before partial pressures of nitrogen and oxygen are calculated.
The starting pressure is set as 1 ata.
The constants ro, gamma, and lambda are set in SUB diveData.
As ro increases, psMin and criticalGradient get smaller, leading to longer decompression times. Substitution of the range of values 0.8 < ro < 1.2 into the code is physically reasonable.
As gamma (= g in Refs. 1 and 2 ) decreases, psMin and criticalGradient get smaller, leading to longer decompression times. Substitution of the range 16 < gamma < 20 into the code is physically reasonable.
My Programs' Constants
The default half-times are Buhlmann's ZHL-16 set: 4.,8.,12.5,18.5,27.,38.3,64.3,77.,109.,146.,187.,239.,305.,390.,498.,635. (min)
The VPM constants are the same as Yount and Hoffman's.
ro = 1 (micron)
gamma = 17.9 (dyne/cm)
lambda = 7180 (fsw min)
Yount and Hoffman's Constants
The eight fastest half-times in ref 1 are: 2,5,10,20,40,80,120,160 (min).
Lambda: l = 7500 (ffw min)
ro = 1 (micron)
Half-times in ref 2 are: 1,2,5,10,20,40,80,120,180,240,360,480,720 (min).
Delta = d --same as Yount's lambda: l-- 7180 (fsw min) = 7502 (feet of freshwater x minutes)
ro = 0.8 (micron)