Unit compatibility (DIR practitioners invited)

[Gombessa]

I've dove with those crazy internationals on a couple of occasions - both instabuddy situations. I was using PSI/feet, but I like ease of using bar/m, and I figure that's the way we'll eventually go, so I'm usually happy to do the conversions and work in bar/meters, especially for these shallow recreational dives. Either way, I'm a fan of agreeing on one system and sticking with it - it avoids a lot of unnecessary confusion.

Since the OP seems to be in the US but working in bar/m, it seems like he'd be the odd man out most of the time, and as such it would probably be more convenient to get used to psi/ft, rather than seeing if every random person he dives with is willing/able to learn an unfamiliar system.

 

[tedtim]

In general, I would say you should adapt to whatever the standard is in the country you are diving in. If you come to the US, and plan on diving with the locals, then I think you should be prepared to do as the local culture requires.

I was working as a DM this summer in Honduras for a British organization. My gauges were set to PSI/ft when I arrived. The courses were being taught in BAR/m. A quick change of the gauges was easy enough to do and it took just a few minutes to change my computer to metres.

The rest was easy. I confirmed communicatons signals that were standard (a few were a bit different than I normally use). All dive briefings were BAR/m.

 

[NudeDiver]

Since the OP seems to be in the US but working in bar/m, it seems like he'd be the odd man out most of the time, and as such it would probably be more convenient to get used to psi/ft, rather than seeing if every random person he dives with is willing/able to learn an unfamiliar system.

More convenient for WHO?

I'm not going to switch

 

[Diver0001]

Take 'em over bro... they have it coming....

R..

 

[NudeDiver]

Take 'em over bro... they have it coming....

Nah. I'm not interesting in forcing my will on anyone, any more than I am in having them force their will on me. I was just curious what other people do about it.

After having read these posts - going from memory, the general summary of responses seems to break down as:

• Go ahead and use different units - just communicate as necessary to make sure you're on the same page.
• One of you really should use the other person's units to ensure you are on the same page.
• Elistist (big surprise) - which I'll paraphrase as, "get with the program", "what, are you so dumb you can't do some math", "how did you ever get certified", "get some memory skills", blah, blah blah.

Specific notes of interest to me:

• Most people seemed to give a thoughtful, useful answer. Some more than others.
• Some people I thought might chime in on the elitist front didn't (kudos to them) - and didn't comment at all actually, but one person I predicted would, did.
• Few broke down their answer the way I requested, but at least one did (Thanks rot).
• The "DIR" answer was surprising - I thought for sure it would be mandatory that people work in the same units, while the units themselves may not matter.
• One person referenced the NASA issue - which is one thing I had in mind when I posed the question (kudos to you!).
• I didn't get the instructor view - for example, instructors who want to teach in one unit, but students who prefer to learn in another - or any sentiment of ASKING students which units they preferred to learn in (which indicates to me that instructors probably don't even consider such preferences).
• No one suggested that you simply show your SPG or computer to your buddy, and let THEM work out the math - which they should be able to do, since we should all be able to do it, right? I can guess why this is (see OP) - but I'm surprised it wasn't put on the table.

I guess that's about it. Thanks to all who participated in my question

 

[Charlie99]

On a normal dive within the NDL's it's a minor issue to calculate with 3 but on a decmpression dive 12 metres (a common stop depth) is 36ft if you work with 3 and 40ft if you work with reality.

You're working things backward. I said 3m = 10', not 1 meter = 3'. 40' is 4 chunks of 10'. 4x3 =12 m.
Or 12 meter/3 = 4 tens or 40'.

Charlie. You're a man of precision. I know you well enough for that. 1 metre is 3.2808399 feet.

That is the correct conversion for lengths, but what we are really talking about is meters-saltwater and feet-saltwater, which are measure of pressure, not length. 1msw is normally defined as 1/10 bar. 1 fsw is normally defined as 1/33 of 1 atm. 1 atm = 1.01325bar. Put that all together and you'll find that 1msw = 3.256 fsw. The approximation of 3m per 10' is equivalent of using 1msw = 3.33... fsw, an error of about 2.5% (or only an error of about 1.4% if we use the meter length to foot length conversion you give of 1m=3.2808399 feet.)

 

[Gombessa]

More convenient for WHO?

My point is just that someone living in the US and working with a non-standard system of measurement will likely face this problem over and over if they dive with a lot of people. And given that most US locals are not as familiar working in bar/m, asking them to use an unfamiliar system, or working with different units, is likely to result in more miscommunication and potentially dangerous mistakes. But it seems like you're pretty well familiar with with psi/ft, and as such it would probably be easier and safer for you to "take the high road" offer to work in that system, especially since you'll likely be faced with that situation often. Otherwise, you'll be asking the same question and dealing with the same issue with every new buddy you dive with.

I'm not going to switch

Nah. I'm not interesting in forcing my will on anyone

If that's your position, it's fine, but it pretty much dictates how the situation will unfold, right? If you're not going to change, it's up to your buddy to decide, and you'll either be dealing with someone who refuses to adopt bar/m when diving with you, or someone who does, and in doing so may or may not be familiar or accurate with it. As long as that's cool with you and your buddy, then that's that.

 

[Diver0001]

Aaahhh.... see? and there I thought you were losing your edge.

For converting in my head I use 3.3 which is easy enough to calculate with. Fortunately after 13 years of using metric I've finally started to get the hang of it.....

Nude, the instructor view: you probably didn't get that because most instructors simply teach what they know. I've never had a mixed class and only one American that I can remember. The signs for 1/2, 1/4, 1/3 are key to communicating pressure and if someone *were* in my class that wanted to dive in Europe then I would insist that they do it in metric for the learning experience. I would assume if you took a class in the States that you would get the same response.

R..

You're working things backward. I said 3m = 10', not 1 meter = 3'. 40' is 4 chunks of 10'. 4x3 =12 m.
Or 12 meter/3 = 4 tens or 40'.

That is the correct conversion for lengths, but what we are really talking about is meters-saltwater and feet-saltwater, which are measure of pressure, not length. 1msw is normally defined as 1/10 bar. 1 fsw is normally defined as 1/33 of 1 atm. 1 atm = 1.01325bar. Put that all together and you'll find that 1msw = 3.256 fsw. The approximation of 3m per 10' is equivalent of using 1msw = 3.33... fsw, an error of about 2.5% (or only an error of about 1.4% if we use the meter length to foot length conversion you give of 1m=3.2808399 feet.)

 

[NudeDiver]

My point is just that someone living in the US and working with a non-standard system of measurement will likely face this problem over and over if they dive with a lot of people.

Unfortunately, there is very little about me that is standard. It's a battle I've fought my whole life ):

But it seems like you're pretty well familiar with with psi/ft

Ah, but I'm not. If I gave that impression, my fault.

If that's your position, it's fine, but it pretty much dictates how the situation will unfold, right?

Again - my intent was to find out about how OTHER people deal with the issue and what they do. It wasn't an inquiry into my own situation, or what I should do

 

[Charlie99]

For converting in my head I use 3.3 which is easy enough to calculate with. Fortunately after 13 years of using metric I've finally started to get the hang of it.....

I find the easiest way to use the factor 3.33333 is to go a factor of three in the "wrong direction", then adjust 1 decimal point.

For example, although meters are bigger than feet, I divide 12 meters by 3 to get 4, then adjust one decimal point to get 40'.

Going the other way: 100' x 3 = 300. Drop a decimal place to get 30 meters.

Conversion to imperial is not something you probably have to do very often, but going the other way is something I do often, since that's the easiest way to go from fsw to atm and ata.