Units of Measure in Diving?

[Belce]

I learned to dive in Imperial and later moved to metric on my dives. I love metric diving and think it works best

Really looking forward to the time the US goes to metric and drops British Imperial system for measurement.

 

[peterbj7]

Britain hasn't used most of the units in the "Imperial system" for many decades/well over a century, and happily mixes old units with metric. Some of what some Americans think is the British Imperial system was actually invented in America and has never been used in Britain.

But you're in Canada anyway. What does it matter to you what the Americans do?

 

[Atom]

Britain hasn't used most of the units in the "Imperial system" for many decades/well over a century, and happily mixes old units with metric. Some of what some Americans think is the British Imperial system was actually invented in America and has never been used in Britain.

But you're in Canada anyway. What does it matter to you what the Americans do?

Being so close to the states, all our equipment is imperial units (PSIs, feet, ...). It's a hard thing to change, everybody is used to imperial. I'm kinda used to both since I've learned abroad and continued diving here, but everybody who learned here is really more familiar with PSIs/feet.

I prefer metric though, makes computations simpler and my computer show depth in 0.1m increments instead of 1 foot increments when set in metric so I find it easier to hold a stop at a fixed depth without a visual reference.

 

[Akimbo]

Britain hasn't used most of the units in the "Imperial system" for many decades/well over a century, and happily mixes old units with metric. Some of what some Americans think is the British Imperial system was actually invented in America and has never been used in Britain.

But you're in Canada anyway. What does it matter to you what the Americans do?

I happened to be doing a lot of work in the UK when they started their official transition to SI in the 1970s. As you would expect, there was plenty of resistance, especially from the older and more skilled craftsman. One machine shop doing some work for me was so fed up by dozens of expensive errors due to conversions inventoried all the Imperial measuring instruments in the shop, including those privately owned. A few weeks later when all the Metric-only replacements arrived, the literally swapped all of Imperial instruments in the shop. The privately owned equipment was locked up for safe keeping in case someone wanted to leave their employ and didn’t want to keep their new "trade".

After about a week of grumbling, it was all over including that big uptick in errors. In all fairness, machinists deal a great deal more with inches and decimal inches so the conversion to Millimeters was pretty simple — decimal units is decimal units.

 

[peterbj7]

Britain had of course been using the SI system for decades before that, mainly in specialist scientific and engineering circles. It had been an integral part of school education for a long time, if only because it was the standard system only 22 miles away across the Channel.

I remember one job I had as an early consultant, working for a steel yard which had overnight to convert all its stocks from imperial to metric measure. They wanted to know the most efficient and least costly way of re-designating all their pre-cut lengths of steel. A very difficult job.

What started then, ordered by our new masters the EEC (later to be renamed the EU), was a crash programme of concerting people in their everyday lives to using the metric system. Quite unnecessary in my view and that of many others. At different times it has been illegal (yes, illegal, punishable by imprisonment) to sell apples by the pound or milk by the pint, and there are countless other examples. They never succeeded in ordering us to buy beer in pubs in litres, as I think there would have been mass riots, though they did try. Petrol (gasoline) is now sold by the litre, though since the price is comparable to what it used to be for the gallon people can relate to that more. :depressed:

I have to say the whole thing has been nonsense, dreadfully carried out, and has caused a vast amount of resentment. In schools they even tried suppressing information on the imperial system so that kids would grow up only knowing the metric system. but that didn't work because they saw imperial units all around them as they grew up.

Britain and most countries have changed units before, totally painlessly, the new system being adopted by common acceptance. What is so wrong about this is that it has been forced upon Britain by an unelected occupying power. I don't know why we bothered to defeat Napoleon at Waterloo as his ideas have won anyway.

Still, we in Britain escaped being forced to drive on the right, which he imposed on every country he conquered (the USA drives on the right because of Louisiana), and the whole world escaped the next change he intended forcing on people, the metrication of time.

The silly thing is that from a practical point of view the metric system has three major shortcomings - (1) the units of measure don't relate in any way to people's everyday lives, whereas the older units mostly came into existence by usage; (2) 10 is only used as the base because we have ten fingers. 12 would have been far better as it is divisible by 3; and (3) what is cited as a major advantage of the decimal system, a point you can simply move to change the order of a number, is equally a disadvantage as people make silly mistakes and have no idea they have made them.

 

[Atom]

The silly thing is that from a practical point of view the metric system has three major shortcomings - (1) the units of measure don't relate in any way to people's everyday lives, whereas the older units mostly came into existence by usage; (2) 10 is only used as the base because we have ten fingers. 12 would have been far better as it is divisible by 3; and (3) what is cited as a major advantage of the decimal system, a point you can simply move to change the order of a number, is equally a disadvantage as people make silly mistakes and have no idea they have made them.

Wow... gotta disagree...

1) It's all a matter of everyday use, of course switching between systems is confusing at first but I don't see how a mile relates more to everyday life than a km, why a PSI is more intuive than a bar.

To me celsius is very intuitive, 0 C is water freezing, 100 C is water boiling. A liter is 10cm x 10cm x 10cm of volume, which if occupied by water is also a kg. And 10cm is the lenght of the orange plastic sticks we had in primary school ; )

2) People commonly use base-10 numbers, so unless you want to express all measurements as fractions all the time you'll lose the precision anyway. And nothing prevents you from doing the same in metric, 1/3 of a meter is a perfect expression of a meter divided by 3.

3) If you can't do basic math in metric you won't fare better in imperial. Quickly... How many feets in 3 miles + 456 yards + 63 rods + 2 chains? How many inches in 13 feets and 4 inches? I've seen way more people screw the multiply by 12 required to convert feets to inches than people screw the simple movement of a decimal point, and I'm not even considering all the conversion factors you have to remember between the unit of different magnitudes.

 

[eponym]

Good stuff. Hijack continues.

I worked in London in the early '70s and was fascinated by the lumber yard conversions, first to SI-labeled plywood which replicated the Imperial sizing, which is of course what you need when doing a repair. "2.4 by 1.2 meter sheet? right here, sir."

I don't know why we bothered to defeat Napoleon at Waterloo as his ideas have won anyway.

You are correct that calculations in the Metric system make everything much less mentally challenging. But did you ever stop and ask yourself WHY this system was suddenly deemed necessary?

Good rants, nice irony. Legend holds that Napoleon commanded his engineers to create a logical underpinning (hence "one-millionth of the distance from the equator to the pole") for a new unit of measure which had to be "slightly longer than the English yard." Talk about seeing whose is longest . . .

Using SI on my computer only when I want to practice really really slow ascents,
Bryan

 

[DuboisP]

The silly thing is that from a practical point of view the metric system has three major shortcomings - (2) 10 is only used as the base because we have ten fingers.

just one question
how long is 11.27 % of one once ?
can you measure it with a drawing-rule ?

 

[DuboisP]

Wow... gotta disagree...

1) It's all a matter of everyday use, of course switching between systems is confusing at first but I don't see how a mile relates more to everyday life than a km, why a PSI is more intuive than a bar.

a bar is approximatively 1 kg/cm2 (1.019716, in fact), as intuitive as a PSI

 

[Akimbo]

a bar is approximatively 1 kg/cm2 (1.019716, in fact), as intuitive as a PSI

I think it is fair to say that the vast majority of diving related calculations are based on Standard Atmospheres and linear water depth. It is hard to argue that imperial measurements are simpler overall if you allow for reasonable rounding.

…One Standard Atmosphere equals:

SI Units
101,325 Pascals
101.325 KPa or Kilo Pascals or 1000x
0.101325 MPa or Mega Pascals or 1 Million x
1.01325 Bar
10.0627586096078 Meters of Sea Water
Imperial Units
14.695948775 PSI
33.899524252 Feet of Fresh Water at 4° C
33.014299900156 Feet of Seawater based on a density of 64.1 Lbs/Ft³​

There is some validity that the finer granularity of Feet for depth measurement is useful, until you consider that accuracy on most depth gauges and computers is not good enough to resolve closer than 1 Meter anyway. I find that argument only holds a little water in commercial diving where Pneumo Fathometers are used with large diameter precision gauges with ¼ to 1/10% accuracy gauges.

http://www.scubaboard.com/forums/5366555-post197.html

My story about the conversion to SI in the UK illustrates there is added risk in switching back and forth or converting. However, because the Bars and Atmospheres conversion is plenty close for estimating, dual scale SPGs are one of the few useful mixing of units on a single instrument that has value — IMHO. Arguing with a dive shop that your fill is 20 Bar short of full may not be so effective if all their gauges are in PSI.

However, your depth gauge should match your tables if you are not using a computer and dual-scale depth displays are more confusing and hard to read than helpful.

Keep in mind the poll question is:
What units of measure do you use most (not necessarily prefer) in diving?

I suppose the answer to the "best" units is the one you "think" in. Being off by a factor of 3.28 when mentally estimating gas consumption or decompression is not good for safety or getting the most our of your dives.