Metric versus Imperial System for Diving?

[nimoh]

Another "magic number" to remember. Actually 95 / 2640 ~ 0.034. So the tank factor is 3.4, not 2.8. See? Already a mistake, 2.8 is for high pressure. So in imperial you have to remember high or low pressure, 95, 2640, tank factor.

In metric you have to remember just ONE!!! number - it's the volume in liters, it's a physical measure, can be measured directly, can be guesstimated by just looking at the tank.

See the difference? You just demonstrated the problems of imperial system, how easily errors can happen. And errors like that do happen and they cost.

yes, you caught me. I don't use 95s, so should have done the calculation before posting.

However, you don't need to know high or low pressure, 95 or 2640, so there is just one number to remember, and rounding it off doesn't introduce any significant errors in calculations.

and by the way, I didn't demonstrate any problems with the imperial system, I only demonstrated problems of the Canadian education system

 

[victorzamora]

In imperial it's: 95 / 2640 * 2800 - now tell me how you are going to calculate that in your head? I can't. I can only say that "2800 is bigger than 2640 so it must be more than 95 cubic feet" - that's it.

First of all, tank factor is water volume....kinda. It's the same number and math as in metric.

Secondly, you must SUCK at math. 2800/2640*95 is the volume in cubic feet. It's just a ratio. Underwater, it's WAY more than close enough. Quicker than you can do your mental math, I can mentally tell you you're rockin 100ft3 in them there tanks.

Thirdly, you must suck at diving and dive planning. Under no circumstances have I needed to calculate remaining air volume in the water. Planning and math are at the surface. When do you ever need to recalculate the exact number of "cubic liters" you have in your tank? Ignore the fact that cubic liters requires 9 spatial dimensions.

Fourthly, calling tanks by the air they can hold at rated pressure is great because I don't have to do secondary math when I'm doing gas planning. "I need 240ft3 of gas with reserves for this dive. Let me take two 120s." I like the metric system as well, but you can't say there are no advantages.

 

[agilis]

I'm just hanging around here for the laffs.

There are no other rational reasons.

 

[Diver0001]

I don't think it's a matter of easier; I think it's a matter of primary language.

I think it's a matter of exposure and intensity of that exposure. Like you, I was going to school when the change happened. My exposure to the imperial system was pretty limited. Just what I had learned in school and concepts like miles and gallons. For me the change would be comparable to how it would be if you traveled to another country and had to use different money. A couple of months after the switch I was adjusted.

My father, on the other hand, grew up and had a long career as a millwright where measurements and sizes are core to your thinking. When he came to the Netherlands to help me renovate my new house (yes, he actually did that) after 3 days we had to get someone to send him a tape measure in imperial because he was using mine (in metric) and spending so much time converting measurements, double checking, recalculating and cutting the wrong sizes anyway that we concluded that a 3 day wait for someone to get (in his words) a "real" tape measure to him in the post would save us time in the long run. LOL

In his case, his entire brain, due to long and intensive exposure to imperial thinking had become so natural to him that learning metric was like learning an entirely new skill set.

We actually talked about that and he said something I'll never forget. He thought that Canada made the right decision but it would take 100 years for the dinosaurs to become extinct. He never regretted or begrudged the qualifier "dinosaur". Like me (or me like him) he has a logical brain and just understands that these changes take time. In his way of thinking (and in mine) there is no reason to force people to change.... just don't teach any new people the old system and in 100 years you have all new people and the problem is solved.

R..

 

[Storker]

cubic liters requires 9 spatial dimensions

While cubic feet only requires .3048*9≈3 spatial dimensions, of course

 

[mrdre]

While cubic feet only requires .3048*9≈3 spatial dimensions, of course

Never heard of super string theory? it's 9 spacial dimensions says new level of diving..

---------- Post added October 28th, 2014 at 11:47 AM ----------

...Ignore the fact that cubic liters requires 9 spatial dimensions....

there is no such thing as "cubic liter", genius

 

[Storker]

there is no such thing as "cubic liter", genius

However, if there were, it would require 9 spatial dimensions


liters = cubic decimeters = dm³. Cubic liters = cubic decimeters cubed = (dm³)³ = dm^9

 

[mrdre]

However, if there were, it would require 9 spatial dimensions


liters = cubic decimeters = dm³. Cubic liters = cubic decimeters cubed = (dm³)³ = dm^9

Sure, and if my grandma had a ....

 

[Storker]

calling tanks by the air they can hold at rated pressure is great because I don't have to do secondary math when I'm doing gas planning. "I need 240ft3 of gas with reserves for this dive. Let me take two 120s." I like the metric system as well, but you can't say there are no advantages.

And how many times have you had your tanks filled exactly to rated pressure? "Oops, I got a short fill, lemme see, that's 2800/3000*80cu.ft, that's... uhm..." I'm like, "OK, 280 bar times 10L is 2800L instead of 3000L"

Besides, except mid-summer, I usually lose some 10-20 bar between rigging and descending, just because of the difference in temperature between the inside of my car and the water.

 

[agilis]

And how many times have you had your tanks filled exactly to rated pressure? "Oops, I got a short fill, lemme see, that's 2800/3000*80cu.ft, that's... uhm..." I'm like, "OK, 280 bar times 10L is 2800L instead of 3000L"

Besides, except mid-summer, I usually lose some 10-20 bar between rigging and descending, just because of the difference in temperature between the inside of my car and the water.

None of which is in any way meaningful. If I have 2800psi instead of 3000psi, that is all the information I need to plan my dive. I don't really need to know how that translates into cubic feet or liters. That information is superfluous. I know that I have 14/15ths of the nominal volume, an insignificant difference within any responsible safety margin. More commonly I'll see a hot reading of 3200psi, or 16/15ths of the nominal volume. This does not have the effect of producing the illusion that I'll be able to extend my planned dive time or depth, both of which I will modify on the spot during the dive if conditions, currents, etc., are not as anticipated. The speed at which the little dial moves counter-clockwise is my prime indicator, and I automatically glance down to consult that dial every few minutes. I have no use for digital or remote pressure gauges.

I pity those unfortunates who are deprived of the joys of fractional calculations. The appeal is almost erotic in its intensity.