Units

[lamont]

This has been a very interesting thread. I'm with OneBrightGator
on being stumped why DIR didn't select a single set of units.
I find it fascinating that the DIR guys allow use of imperial units.
I assumed that when given options, the DIR way was to choose
the better/safer/more reliable equipment or ways of doing things.

Ignoring which unit system "feels" better,
Metric seems so much easier and simpler to do calculations
especially if you are having to them in your head.

So if metric is easier and simpler to do calculations or
re-calculations while diving, doensn't that make it safer?

And if its safer, why would DIR not chose the "better"/"simpler"
and less error prone system?

Just curious.....

--- bill

Fix problems actually encountered underwater.

I've never had a near miss due to doing calculations in imperial units.

 

[Kevrumbo]

Just started getting used to diving a Vytec in Imperial and a D3 in Metric; makes figuring your Ata calculation at depth much quicker, and your Gas Consumption reckoning a little easier (especially for multi-level dives). . .

 

[Reinoud]

I'm one of those rare birds in the US since, with science training, I'm equally comfortable in metric and imperial. When it comes to the math needed for diving, I don't really see one as easier than the other, or less error-prone.

See "Beyond the daylight zone - the Fundamentals of cave diving" (the Cave 1 manual), page 57 (chapter 6.2).
The calculation to know how much gas is in a tank takes 12 lines to explain in imperial, the metric one 6 lines.

 

[lamont]

See "Beyond the daylight zone - the Fundamentals of cave diving" (the Cave 1 manual), page 57 (chapter 6.2).
The calculation to know how much gas is in a tank takes 12 lines to explain in imperial, the metric one 6 lines.

i've never seen so much optimizing for out-of-water convenience in the DIR section...

 

[radinator]

See "Beyond the daylight zone - the Fundamentals of cave diving" (the Cave 1 manual), page 57 (chapter 6.2).
The calculation to know how much gas is in a tank takes 12 lines to explain in imperial, the metric one 6 lines.

I'll have to look. Perhaps it's poorly written.

I have a 3500 psi HP100 tank (which is 100 cubic feet at 3500 psi).

If I have 1800 psi in it, I have approximately 50 cubic feet.
If I have 1000 psi, I have 2/7th of 100, or 28 cubic feet.
If I have 500, I have 1/7th, of 100, which is 14.
This was done as fast as I can type, no calculator. It's trivial.

However, when diving, unless you are using a lift bag, there's no immediate point in calculating the volume of the gas. Instead, you want to know things like "How much am I going to use in the next 10 minutes?" That question could be answered in units of volume, but since the SPG works in pressure it makes more sense to answer in pressure units directly.

So, I'm at 80' sea water, which is just under 3.5 ATA. I know my psi/min SAC, so I do SAC x 3.5 x 10. Again, not hard. There is no reason to go into the 'volume' units at all here.

Don't get me wrong, in theory having everyone in the world work the same units is a reasonable goal. However, having people work in units that they do not have an intiutive feel for is just asking for errors. And no scuba training is going to cause someone to have the intuitive 'feel' for the units if they haven't learned those units in their everyday life.

I suspect the GUE gurus have had this discussion at some point, and decided against it, probably for a list of reasons including the point I'm making.

I am curious though what the metric equivalent of the 'rule of 120' is. For those who don't know imperial, it is 'depth + time = 120', which gives an approximation of NDL. Depth in feet and time in minutes. Is it 'depth_in_meters* 3.3 + time_in_minutes = 120' or is there another equivalent? I really don't know and am curious.

 

[Azotino]

Heh. The metric system. For all 12 years of public school I attended, I was taught the metric system. It was widely acknowledged that the USA would be going metric. Right after I graduated, I got a job in construction. I was lost- I didn't know how many inches were in 8 feet or what a sixteenth of an inch was. 22 years later, and imperial units are burned into my soul; the metric system is just another useless thing they wasted my time with in school, like when they made us read "Wuthering Heights".

OK, so it's not useless(The metric system, I mean. "Wuthering Heights" is 100% useless.) I fully understand that Metric is superior to imperial, but we failed to switch over, and we probably never will. Sheets of plywood and sheetrock are still 4 feet by eight feet, and EVERYTHING is built out of plywood and sheetrock. I guess we'll just have to look at it like languages or something. If I want to go dive in Germany, I'll probably have to learn some German, and brush up on my metric conversions, too.

Plywood and sheetrock are in imperial ......mechanical staff are in metric.
Which is the big problem???? They are so simple , both.
They are no superior no inferior......you need just a little patience to learn both.
Nothing learned in school is useless........

 

[dherbman]

Plywood and sheetrock are in imperial ......mechanical staff are in metric.
Which is the big problem???? They are so simple , both.
They are no superior no inferior......you need just a little patience to learn both.
.

Yeah, tell it to NASA.

 

[radinator]

If DIR is supposed to be a "globally viable solution" then sooner or later people are going to end up diving a system they´re not "feeling".

When I travel, I take my regs and my bottom timer. I can dive imperial even in Europe. *gasp*

 

[Azotino]

Yeah, tell it to NASA.

That isnt a metric problem...that is called USER ERROR....or some others words like Stu@@@@.

 

[Azotino]

But that´s an argument FOR teaching it in class, not against it...

If DIR is supposed to be a "globally viable solution" then sooner or later people are going to end up diving a system they´re not "feeling". Instead of choosing one system and giving people a chance to use it during class, GUE leaves divers having to fend for themselves when they encounter the "real world". Which, using radinators words, makes for a lot of error prone dir-divers...

That´s hardly optimal, is it?

DIR isn't a "globally viable solution".....this is a classical example

Some parts of the world use Metric some others use Imperial