Metric vs Imperial

[Tigerman]

My point exactly. Knowing that you use 2 bar/minute is pointless - unless you know the tank capacity or never dive a tank with a different capacity.

 

[Kevrumbo]

My point exactly. Knowing that you use 2 bar/minute is pointless - unless you know the tank capacity or never dive a tank with a different capacity.

The most common & ubiquitous tank used at all destination dive-ops around the world IS the AL80/11L tank. That's the single tank & twinset I mostly use wherever I go --and 2 bar/min is not pointless and understood in my post above, to be relative to the AL80/11L tank. For any other metric tank ratings, simply do the math . . .

Does that clarify things better? Anyway, it's all easier using Metric System. . .

 

[Tigerman]

Ive been saying do the math, but to do the math you have to know the volume of the tank you use 2 bar/minute with in the first place.
To get from 2 bar/min on your 12l tank to what youll use out of a 15l tank you go to liters/min (24) and back to the 1.6 bar/min that translates to with a 15l tank..
The liters/min is your "absolute" to the extent there is such a thing given your consumption change with conditions, but the bar/min is even less constant given it change with tanks as well.

Regardless its much easier to work with liters and bar than psi and cu/ft given the very simple metric math of 1 bar = 1x liters volume of tank and 10m = 1 atm/close enough to bar pressure..

 

[Hatul]

The metric system is better it's true and easier to work with, but with mobile computers and calculators being so ubiquitous it's not that big a deal to convert.

 

[Tigerman]

My iPod is not waterproof

 

[pjhansman]

Canada is all metric except for seemingly everything to do with diving - tank size, tank pressure, depth...

.....and everything to do with construction (try buying a metric 2"x4")

I've been watching Canada trying to convert to metric for several decades. Until the USA switches, the imperial system ain't going away in a hurry.

 

[Tigerman]

2x4, 2x2, 2x6, 4x6 and so on is sizes used all over the world. Theire also sizes normally used for framing, beams and so on and i would guess the main reason why the sizes has stuck all over the world (im not a carpenter) is that they are proper dimensions for the different uses where they are normally used and as such they just kept using the same name as well as dimensions?

I think ill be starting to use binary when I go to the hardware store instead... I need 101 meters of 010x100 please..

 

[Kevrumbo]

Ive been saying do the math, but to do the math you have to know the volume of the tank you use 2 bar/minute with in the first place.
To get from 2 bar/min on your 12l tank to what youll use out of a 15l tank you go to liters/min (24) and back to the 1.6 bar/min that translates to with a 15l tank..
The liters/min is your "absolute" to the extent there is such a thing given your consumption change with conditions, but the bar/min is even less constant given it change with tanks as well.

Regardless its much easier to work with liters and bar than psi and cu/ft given the very simple metric math of 1 bar = 1x liters volume of tank and 10m = 1 atm/close enough to bar pressure..

As I stated above, your volume SCR (also known as RMV -Respiratory Minute Volume) is the "arbitrary" constant across all metric tank ratings ("Arbitrary" in this instance because like you said, consumption rate depends on environmental conditions, physical fitness, workload etc). In my example above, the goal is to utilize a pressure SCR that is commonly understood to be predicated on the metric tank rating in use, because your SPG is is in bar pressure units --NOT volumetric liter units.

You misunderstand my example and trying to make an argumentative point that is moot: I'm not saying to start with 2 bar/min pressure SCR to figure corresponding pressure SCR values across all metric tank values --that is incorrect! You always start the calculations with your volume SCR (RMV) value. The pressure SCR to use is whatever value of dividing your volume SCR (RMV) by the metric tank rating in litres/bar of the particular tank you're using.

Again for example, with a 22 l/min RMV (same as volume SCR) and a variety of different tank sizes, your pressure SCR in bar/min obviously varies inversely, depending on the size tank in use :

22 litres per minute -divided-by- 11L/bar tank (AL80): 2 bar/min
22 litres per minute -divided-by- 13L/bar tank (AL100): 1.7 bar/min
22 litres per minute -divided-by- 22L/bar twinset (double AL80's): 1 bar/min
22 litres per minute -divided-by- 34L/bar twinset (double Pressed Steel 104's with a cave fill): 0.7 bar/min

And finally again, an example of how to gas plan on-the-fly using 22 l/min with the 11L/AL80 tank (post #5 above) with easier more intuitive metric units: http://www.scubaboard.com/forums/non-diving-related-stuff/441101-metric-vs-imperial.html#post6572242

 

[drrich2]

I dealt with the metric system extensively in science classes in college, and of course it was very useful there.

But out in the 'real world,' I use imperial most of the time. I was raised with imperial units, and have a lifetime of ingrained intuitive examples of their meaning. If you tell me a metric measure, I have to convert it to imperial mentally to make sense of it.

I recall a liter is a little more than a quart, a kg ~ 2.2 lbs, a km ~ 0.6 miles, 1 ft ~ 30 cm, 1 inch ~ 2.54 cm, and while I never could convert Celsius, I know water freezes at 0 (so 32 degrees), boils at 100 (so 212 degrees), and science labs tended to be 25 degrees or 20 (with 20 being a tad cool), and if memory serves 30 something is hot.

Our culture strongly reinforces imperial in our day-to-day lives. Also, we measure in feet a lot, and there seems no really common metric equivalent; I don't like giving lengths in cm or fractions of a meter. So I have to translate metric as a 'second language.'

It's also noteworthy much of the U.S. population doesn't do unit mathematical conversions often. Converting between inches, feet & to a lesser extent yards is about the extent of it. So imperial is 'good enough' for them, and they already know it.

And here's a thought...why does the scientific community still use the non-ten-based time system? Instead of a 24 hour day with 60 seconds/minute, 60 minutes/hour, why haven't they switched to 'centi-days' (1/100'th of a day, or about 14.4 minutes?) and millidays (1.44 minutes)?

Richard.

 

[Mr. Willoughby]

I've been seriously considering switching all my gear and computer settings to metric units. It is just easier to use a ten base system despite having twenty years of diving in imperial... Ask me what the water temp is and you'll get a metric answer but the wreck is 150 metres out and she lies at 90 feet...

Seriously, aside for knowing water freezes at 32 degrees F. and a fever is over 97 F. I am completely lost with temperature... I'm not too bad with distance though as I and everyone I know still give height in feet but I can use centimetres and metres just as well.