> On Jul 5, 2015, at 4:29 AM, Rick Walsh <[email protected]> wrote: > > I am not really familiar with diving in imperial system but this patch seems > quite specific. Could somebody please check that this problem really only > affects the MOD of EAN100 and not other standard gases? I checked EAN50 (21m > = 70ft) but I don’t know what people expect. For example what do imperial > users list as MOD of EAN36 (being a quite common gas), 100ft or 110ft? > According to our formula it is 108ft.
EAN36 has a MOD of 114ft and that's what people would write on their tank / regulator. 1.6 / 0.36 = 4.44 3.44 * 33 = 113.52 -> 114ft MOD > I don’t know what to do is right. Somehow, for deco calculations it seems > 1ft=30cm exactly (which would give 10ft/3m deco step intervals) or we could > fudge a bit with the maximal pO2 in imperial mode so it comes out like this. > > I've never dived using feet to measure depth either. Perhaps we can ask one > of our friends from Liberia, Burma, or that other country that still would > rather divide by 3, 12 and 1760 than 10 and 1000. But who are we to judge? > There's nothing special about 3 m, we're the muppets using ~10ft deco stop > increments when we don't even measure in feet. I learned diving in one of those retarded countries and while I grew up with the metric system I still tend to use and think imperial when diving. > But, we should do something, calculating the default MOD of oxygen as 10ft > goes against expected behaviour. At a minimum, we should fix it for this > gas, because it is commonly used. > > One possible fudge would be to say that 1.60 bar = 1.62 bar. I thought about > it, but don't really like it. I'm unlikely to dive with anything other than > 100%, 80% and/or 50% nitrox for deco in the near future, but I believe the > following is a list of fraction O2 for standard/common deco gasses, and > calculated MOD based on pO2 = 1.6 bar, and usual/standard adopted MOD for the > gas. > > Mix MOD (m) @1.6 MOD (std) (m) MOD (ft) @1.6 MOD (std) (ft) pO2 at > std ft pO2 at std m > 100%* 6 6 19.7 20 1.61 1.60 > 80% 10 9 32.8 30 1.53 1.52 > 50%* 22 21 72.2 70 1.56 1.55 > 36% 34.4 33 113.0 110 1.56 1.55 > 35/25* 35.7 36 117.2 120 1.62 1.61 > 32% 40.0 39 131.2 130 1.58 1.57 > 21/35* 66.2 57 217.2 190 1.42 1.41 > *GUE standard mix > > My patch works for 100%, but not for 35/25 or 21/35. Looking at that table, > it appears the best rounding method would actually be "round to nearest 3m / > 10ft", rather than rounding down as we currently do. No amount of rounding > will give 21/35 an MOD of 57 m / 190 ft. > > Another option would be to have special cases for gas with 100%, 35% and 21% > oxygen. Special cases seems wrong. That's what I didn't like about your patch. But what I've seen in diver training and in blender training (I'm a certified trimix diver and trimix blender) is that you round to the nearest foot. Not truncate. So this gives you 20ft for 100% I don't know of a blender who would write down 120ft as MOD 35/25, nor of someone who'd suggest 190ft for 21/35. So these I would classify as GUE oddities. I'll happily take a patch that rounds to the nearest foot in imperial and that should solve the one annoyance we currently have. /D
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