<div dir="ltr">Hi Robert,<br><div><div class="gmail_extra"><br><div class="gmail_quote">On 5 July 2015 at 16:18, Robert C. Helling <span dir="ltr"><<a href="mailto:helling@atdotde.de" target="_blank">helling@atdotde.de</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Hi Rick,<br>
<br>
> On 05 Jul 2015, at 01:41, Rick Walsh <<a href="mailto:rickmwalsh@gmail.com">rickmwalsh@gmail.com</a>> wrote:<br>
><br>
> <0016-MOD-of-oxygen-at-pO2-of-1.6-is-20ft.patch><br>
<br>
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.<br>
<br>
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.<br></blockquote><div><br></div><div>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.<br><br></div><div>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.<br></div><div><br></div><div>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.<br><br>
<table border="0" cellspacing="0">
<colgroup span="7" width="85"></colgroup>
<tbody><tr>
<td align="left" height="17">Mix</td>
<td align="left">MOD (m) @1.6</td>
<td align="left">MOD (std) (m)</td>
<td align="left">MOD (ft) @1.6</td>
<td align="left">MOD (std) (ft)</td>
<td align="left">pO2 at std ft</td>
<td align="left">pO2 at std m</td>
</tr>
<tr>
<td align="right" height="17">100%*</td>
<td align="right">6</td>
<td align="right">6</td>
<td align="right">19.7</td>
<td align="right">20</td>
<td align="right"><b>1.61</b></td>
<td align="right">1.60</td>
</tr>
<tr>
<td align="right" height="17">80%</td>
<td align="right">10</td>
<td align="right">9</td>
<td align="right">32.8</td>
<td align="right">30</td>
<td align="right">1.53</td>
<td align="right">1.52</td>
</tr>
<tr>
<td align="right" height="17">50%*</td>
<td align="right">22</td>
<td align="right">21</td>
<td align="right">72.2</td>
<td align="right">70</td>
<td align="right">1.56</td>
<td align="right">1.55</td>
</tr>
<tr>
<td align="right" height="17">36%</td>
<td align="right">34.4</td>
<td align="right">33</td>
<td align="right">113.0</td>
<td align="right">110</td>
<td align="right">1.56</td>
<td align="right">1.55</td>
</tr>
<tr>
<td align="right" height="17">35/25*</td>
<td align="right">35.7</td>
<td align="right">36</td>
<td align="right">117.2</td>
<td align="right">120</td>
<td align="right"><b>1.62</b></td>
<td align="right"><b>1.61</b></td>
</tr>
<tr>
<td align="right" height="17">32%</td>
<td align="right">40.0</td>
<td align="right">39</td>
<td align="right">131.2</td>
<td align="right">130</td>
<td align="right">1.58</td>
<td align="right">1.57</td>
</tr>
<tr>
<td align="right" height="17">21/35*</td>
<td align="right">66.2</td>
<td align="right">57</td>
<td align="right">217.2</td>
<td align="right">190</td>
<td align="right"><b>1.42</b></td>
<td align="right"><b>1.41</b></td>
</tr>
</tbody></table>
*GUE standard mix<br></div><div><br></div><div>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.<br><br></div><div>Another option would be to have special cases for gas with 100%, 35% and 21% oxygen.<br></div><div><br></div><div>Cheers,<br><br></div><div>Rick<br></div><div><br></div></div></div></div></div>