PSI or BAR in Tech diving?

[TSandM]

I can actually do conversations from psi/bar and from feet/meters in my head underwater. Danny made sure of that . . .

 

[String]

If fact, isn't 3m simply a crude approximation of 10ft?

No more than 10ft is just an arbitrary decision someone took back in the days of analogue gauges where reading any less than that was fairly difficult.

3m isn't a standard. Its just that convention has been implemented into software to fit that. Its arbitrary. They could also have put 5ft, 11ft, 15ft or 27.34632ft. The model would still work. There is no physics that says 10ft/3m has to be done.

I've often wondered why those doing stage deco diving with meter depth gauges haven't demanded software that delivers stops in 5m increments.

Why bother when all gauges read to within 0.1m ? Could also say why don't people use 20ft software demand on imperial gauges. Again, there's no reason to.

 

[Blackwood]

No more than 10ft is just an arbitrary decision someone took back in the days of analogue gauges where reading any less than that was fairly difficult.

3m isn't a standard. Its just that convention has been implemented into software to fit that. Its arbitrary. They could also have put 5ft, 11ft, 15ft or 27.34632ft. The model would still work. There is no physics that says 10ft/3m has to be done.

.

Agreed. That was my point exactly.

 

[Ste Wart]

To try and steer this thread mildly back onto topic.

Can someone give an example of gas calculation using imperial? Nothing fancy.

Lets say the best mix for a 100/300' dive.
O2 to be a max of 1.2pp
And and Equivalent Narcotic depth of 40m/120'

 

[Spazzy]

Metric is the obvious choice. Quite apart from the convenience of working in base 10 it is also universal - well almost, in that U.S.A, Liberia, and Burma are the only countries still persisting with the imperial system of measurement.

 

[boulderjohn]

It would be wonderful if all divers used the same system, and metric would logically be the one to use because it is so much easier in general.

However, the same would be true for everything in our lives in which the two systems are possible. If the U.S. and Liberia would fully adopt the metric system, things would be so much better. However, that is not going to happen in my lifetime at least, so I don't see any point in discussing it. I use imperial for almost everything else I do in life. All my friends use imperial. Most of the places I visit for diving use imperial. Any argument I make for the contrary would be like pi$$ing into the wind.

 

[Blackwood]

Metric is the obvious choice. Quite apart from the convenience of working in base 10

That's right, imperial is binary. I have 110101110010 PSI of gas.

 

[boulderjohn]

That's right, imperial is binary. I have 110101110010 PSI of gas.

I know you were joking, but as I recall from my history, the imperial system is derived in large part from the Vikings, who used a base 12 system. That is why we have so many 12s in our lives (time of day, inches in a foot, people on a jury, etc.).

Don't confuse this with the Minnesota Vikings, who use a base 11 system.

 

[Blackwood]

To try and steer this thread mildly back onto topic.

Can someone give an example of gas calculation using imperial? Nothing fancy.

Lets say the best mix for a 100/300' dive.
O2 to be a max of 1.2pp
And and Equivalent Narcotic depth of 40m/120'

300 ft is about 10ATM (3 for every 100' hydrostatic plus atmospheric).

PO₂=FO₂*P
1.2ATM/10ATM=FO₂=.12

END=(D+33)*(1-FHe)-33
120=333*(1-FHe)-33
.459=(1-FHe)
.54=FHe

So your gas is 12/54

I use standard gases rather than compute best mixes, so my math may be rusty. Either way, it's the same workflow as using the metric system. Only differences are the units and the height of one ATM of water (33ft or 10m).

It would be wonderful if all divers used the same system

Definitely. And that may be an easier change than getting nations to adopt new standards. You'd only have to petition dive agencies. The way DOT tanks are stamped could easily be covered with some math (or more likely references tables).


I still don't see it happening, though, so I'll do my best to remain flexible.

Don't confuse this with the Minnesota Vikings, who use a base 11 system.

Interesting, I didn't know that history. If I watched football, would I get that last bit?

 

[mikemill]

I know you were joking, but as I recall from my history, the imperial system is derived in large part from the Vikings, who used a base 12 system. That is why we have so many 12s in our lives (time of day, inches in a foot, people on a jury, etc.).

Don't confuse this with the Minnesota Vikings, who use a base 11 system.

Interesting. I thought the reasons for so many 12s was because of its large number of divisors compared to 10