Metric versus Imperial System for Diving?
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Emphasized for irony. A gram has never been a unit of weight. A gram is, and has always been, a unit of mass. Unlike the lb, which can be either lbm or lbf...
The pond, OTOH. One pond is the downward force exerted by one gram at one standard g. Similarly, the kilopond (kp) is the downward force exerted by one kilogram (kg) at one standard g, i.e. the weight of one kg at the earth's surface. However, since the numbers are identical, the shorthand notation "kilo" was used regardless of whether the unit was a kg or a kp, and since most people knew the kilogram, but not the kilopond, they used the weird unit kg/cm² (mass per area) for pressure instead of the correct unit kp/cm² (force per area).
Not in everyday life. Can you notice a temperature difference of less than 1°C (~2°F)? I can't. For everything else, there's decimals.
And the point isn't whether or not a given unit is insufficiently granular, too granular or just right. It's the system, with its powers of ten for every-effing-conversion that counts. The fact that one atmosphere ≈ 1 bar ≈ 1 kp/cm² is just a nice bonus.
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Which is why one initially assumes that even the USA ought to be able to understand and use it. However...
EDIT:
I always hate it when I look up scientific or engineering data in old publications and find that they're given in archaic units like lbs/in², BTU/h or furlongs per forthnight. One of the wonderful properties of the (metric) SI system of units is that if you input your data in SI units, your output is in SI units. No intermediate conversions, no fudge factors. It's a wonderfully simple way of ensuring that your result isn't off by an American mile or twenty-seven because you forgot to input the correct conversion factors.
I'd wager a bet that if the NASA had used metric units all the way, the Mars Climate Orbiter would have performed as intended.
EDIT2:
For the benefit of you metrically challenged, I give you the obligatory XKCD comic:
Last edited:
oszillodrom
Contributor
That's exactly what happened:
"However, on September 23, 1999, communication with the spacecraft was lost as the spacecraft went into orbital insertion, due to ground-based computer software which produced output in non-SI units of pound-seconds (lbf×s) instead of the metric units of newton-seconds (N×s) specified in the contract between NASA and Lockheed. The spacecraft encountered Mars on a trajectory that brought it too close to the planet, causing it to pass through the upper atmosphere and disintegrate."
Costs: hundreds of millions of $.
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mrdre
Contributor
NASA uses metric system everywhere.. It's just programmers used inches on their own. I guess if NASA outsourced these jobs this wouldn't have happened..
Mustard Dave
Contributor
In the UK, we are a bit funny with our units. I'm 35 and have always been taught in metric units, so you'd expect the older folks to have got used to them. Food has always been weighed out in pounds, but in recent years, this has been outlawed. Food has to now be sold in metric units and there was outrage when it happened as none of the coffin dodgers had a clue what a kilogram was. It is still permitted to advertise a price in imperial units, but it must be secondary to the metric price. Despite this, you can still buy a quarter pounder from McDonalds, a 12" Italian BMT from Subway and pizzas are advertised by diameter in inches.
Clothes are still sized in inches and we tend to refer to somebody's height and weight in feet and inches, and stones and pounds. We also tend to use miles for long distances and speed limits are still in miles per hour.
At work, I have always worked in metric. Like most I can work in both, but I prefer metric. Most of the older boys can do the same but often default to imperial units. Some just stubbornly refuse to work in metric though. Recently I was buying some plasterboard. Building materials such as this traditionally come in 8' X 4' sheets, but with metrication, things tend to be sold by the nearest round number in metric, so the stuff I wanted is now sold as 2400mm X 1200mm, which is slightly smaller. I went to a local builders' merchant and asked for 2400mm by 1200mm sheets and he looked at me like I was talking foreign - "The ones we sell are eight by four...". I said that would be fine and they delivered them the next day. I noticed the sheets are all stamped 2400mm X 1200mm. I enquired at the same place about prices for skirting board and it was £1.32+VAT per metre!
Money is an odd one. Before decimalisation (43 years ago), there was 240 pence to the pound. Multiples of pence were referred to by all sorts of names, such as florins, crowns, half crowns, shillings sixpence, thrupenny, ha'penny etc. When decimalisation came in, there were now 100 pence to the pound. With the exception of those who live in parts of Norfolk, most of us have ten fingers, so a base 10 system should be a piece of piss, but many still struggled and some still do.
The shilling was 12 pence, so there used to be twnty to the pound. The new five pence piece was a similar size and weight, and there are also twenty to the pound, so this became known as the shilling, or 'bob' by its slang term. If something is £4.60, my dad will say 'four pound and twelve bob', whereas I would say 'four pound sixty'. Why people insist on working out how many times five goes into the number after the decimal is beyond me.
With diving though, I have always used bar, kilograms , litres and metres. A cylinder is always measured by its volume at atmospheric pressure. The reasons why this is the best system have been explained several times.
I have never met a diver who uses psi, cubic feet and feet - even the older ones. One thing that bugs me is there are loads who still work out their weight requirement in pounds. Most of the instructors I know do it and even people my age and younger. A slightly hilarious (but at the same time dangerous) incident occurred on our annual club trip to Malta. It was my turn to organise it, so I arranged the diving with a dive centre we have used for the past four years. A lot of the diving in Malta can be done from the shore as it gets deep very quickly, but a few sites can only be reached by boat. There were two boat dives we wanted that were both around 40m, so we decided to do them over two days so we didn't get stung by deco doing them on the same day.
Usually we do the first dive at Cirkewwa. There are two artifical reefs with a sea bed of 34m. The entry point is a shallow rock pool that then opens up into the sea. It is an ideal first dive as it is great for doing a weight check. The owner of the dive centre emailed me to say the only days the boat was available was days one and two. I looked at the list and there was nobody who this should have been a problem for. All were experienced cold and warm water divers and all had either a tech or professional qualification. I did however send out an email to the group to tell them the first dive would be straight off a boat and down a shot-line to 35-40m, and they should either think what weight they last used in their wetsuits, or come for a bracing dip in Wales before travelling.
On the first day, one of the group (PADI instructor) asked me on the boat what site we were doing. "The Imperial Eagle." I replied. "Off the boat and there's a permanent shot. Down the shot to the statue of Christ at 30m and then swim around the corner of the rock to the wreck.". He then told me he hadn't been in open water for nearly a year, but I pointed out I did send an email warning people there would be no check dive. He kitted up though and just got on with it.
His buddy was a regular to Malta. He was a BSAC Dive Leader and also had his advanced nitrox and extended range, so roughly similar to a PADI DM with a Tec 50 cert. The two of them jumped in first, and I was one of the last in. As I swam for the shot, the two of them were swimming back, with the second diver looking distressed and the first towing him. I watched them onto the boat and waited for an 'okay' signal. On the signal, my buddy and I descended.
I spotted the two divers had made it back into the water as they were on the wreck. Big 'okay' signal and both looking happy. Back on the boat, I went to see they were okay:
"Yeah, I'm fine. It was these weights", he said?
"Yeah?", I replied.
"Yeah! I need sixteen pounds and they had two 'stamped' on them, so I took eight."
What I wanted to say would probably upset the ScubaBoard swear-filter so much it would alert the pope if I typed it. Because I'm nice, I just said, "They're two kilo, not two pounds.".
"Yeah! I know that now..."
Clothes are still sized in inches and we tend to refer to somebody's height and weight in feet and inches, and stones and pounds. We also tend to use miles for long distances and speed limits are still in miles per hour.
At work, I have always worked in metric. Like most I can work in both, but I prefer metric. Most of the older boys can do the same but often default to imperial units. Some just stubbornly refuse to work in metric though. Recently I was buying some plasterboard. Building materials such as this traditionally come in 8' X 4' sheets, but with metrication, things tend to be sold by the nearest round number in metric, so the stuff I wanted is now sold as 2400mm X 1200mm, which is slightly smaller. I went to a local builders' merchant and asked for 2400mm by 1200mm sheets and he looked at me like I was talking foreign - "The ones we sell are eight by four...". I said that would be fine and they delivered them the next day. I noticed the sheets are all stamped 2400mm X 1200mm. I enquired at the same place about prices for skirting board and it was £1.32+VAT per metre!
Money is an odd one. Before decimalisation (43 years ago), there was 240 pence to the pound. Multiples of pence were referred to by all sorts of names, such as florins, crowns, half crowns, shillings sixpence, thrupenny, ha'penny etc. When decimalisation came in, there were now 100 pence to the pound. With the exception of those who live in parts of Norfolk, most of us have ten fingers, so a base 10 system should be a piece of piss, but many still struggled and some still do.
The shilling was 12 pence, so there used to be twnty to the pound. The new five pence piece was a similar size and weight, and there are also twenty to the pound, so this became known as the shilling, or 'bob' by its slang term. If something is £4.60, my dad will say 'four pound and twelve bob', whereas I would say 'four pound sixty'. Why people insist on working out how many times five goes into the number after the decimal is beyond me.
With diving though, I have always used bar, kilograms , litres and metres. A cylinder is always measured by its volume at atmospheric pressure. The reasons why this is the best system have been explained several times.
I have never met a diver who uses psi, cubic feet and feet - even the older ones. One thing that bugs me is there are loads who still work out their weight requirement in pounds. Most of the instructors I know do it and even people my age and younger. A slightly hilarious (but at the same time dangerous) incident occurred on our annual club trip to Malta. It was my turn to organise it, so I arranged the diving with a dive centre we have used for the past four years. A lot of the diving in Malta can be done from the shore as it gets deep very quickly, but a few sites can only be reached by boat. There were two boat dives we wanted that were both around 40m, so we decided to do them over two days so we didn't get stung by deco doing them on the same day.
Usually we do the first dive at Cirkewwa. There are two artifical reefs with a sea bed of 34m. The entry point is a shallow rock pool that then opens up into the sea. It is an ideal first dive as it is great for doing a weight check. The owner of the dive centre emailed me to say the only days the boat was available was days one and two. I looked at the list and there was nobody who this should have been a problem for. All were experienced cold and warm water divers and all had either a tech or professional qualification. I did however send out an email to the group to tell them the first dive would be straight off a boat and down a shot-line to 35-40m, and they should either think what weight they last used in their wetsuits, or come for a bracing dip in Wales before travelling.
On the first day, one of the group (PADI instructor) asked me on the boat what site we were doing. "The Imperial Eagle." I replied. "Off the boat and there's a permanent shot. Down the shot to the statue of Christ at 30m and then swim around the corner of the rock to the wreck.". He then told me he hadn't been in open water for nearly a year, but I pointed out I did send an email warning people there would be no check dive. He kitted up though and just got on with it.
His buddy was a regular to Malta. He was a BSAC Dive Leader and also had his advanced nitrox and extended range, so roughly similar to a PADI DM with a Tec 50 cert. The two of them jumped in first, and I was one of the last in. As I swam for the shot, the two of them were swimming back, with the second diver looking distressed and the first towing him. I watched them onto the boat and waited for an 'okay' signal. On the signal, my buddy and I descended.
I spotted the two divers had made it back into the water as they were on the wreck. Big 'okay' signal and both looking happy. Back on the boat, I went to see they were okay:
"Yeah, I'm fine. It was these weights", he said?
"Yeah?", I replied.
"Yeah! I need sixteen pounds and they had two 'stamped' on them, so I took eight."
What I wanted to say would probably upset the ScubaBoard swear-filter so much it would alert the pope if I typed it. Because I'm nice, I just said, "They're two kilo, not two pounds.".
"Yeah! I know that now..."
dfx
Contributor
So you don't get it either. "$3.24 9/10" is not only mathematically incorrect, it is also something that only people with an imperial mind would come up with. It's also completely redundant. Correct would be writing it as $3.249 (which is what you'd see in Europe), but apparently this would confuse the average American. Or you could write it in cents, as 324.9 (as Canadian gas stations do). Of course you could also write it as 324 9/10 cents, but why? It's a waste of space. Either way, $3.24 9/10 is complete nonsense.
Aquavelvet
Contributor
Odd, I recently returned from a trip to Thailand and the Philippines. Weights in both countries were marked in pounds. I believe the lead molds used to make the weights were all originally in pounds.
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dfx
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We've been using metric units almost exclusively for the last century or so, but we still find weights in pounds in the stores, at least the belt weights. Except the smallest ones. So I have 1kg, 4# and 6# weights for my weight belt.
Most people call the 4# weights 2kg and the 6# weights 3kg, though. Even if there's a 10% difference.
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