### Author Topic: Use of Metric Units  (Read 20506 times)

#### edzieba

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##### Re: Use of Metric Units
« Reply #60 on: 10/17/2023 10:02 am »
But there are a couple of other reasons, too.  It's convenient that the density of water is 1 g/cm3 and that the polar circumference of the earth is 40,000 km (quick: what are the equivalent values in imperial units?).
The equivalent imperial unit is the nautical mile.  One km is one centigradian* of latitude.   One nautical mile is one minute of latitude.

I wouldn't say it's the equivalent imperial unit, because it has nothing to do with the definition of the foot and is used only in specialist applications.

Agreed.  A nautical mile is by definition equal to one minute of latitude and is not really equivalent to any other distance measurement.

Being outside of the influence of both the US and Europe, us over here Down Under get to pick and choose to the level of insanity sometimes - hence distance in either km or nautical miles (but not both for the same measurement) and altitude in feet!

You get used to it...
At least you chaps managed to banish that abominable 'centi' prefix from your colloquial measurements and stuck with pure 103 scaling when you went through metrification.

#### daedalus1

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##### Re: Use of Metric Units
« Reply #61 on: 10/17/2023 10:16 am »
By the way 'meter' should be spelt metre.
A meter is something you measure flow rate e.g. water meter.

#### Emmettvonbrown

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##### Re: Use of Metric Units
« Reply #62 on: 10/17/2023 03:38 pm »
Born in the country which invented the metric system. Still, managed to survive pound, feet, inch, and miles - with Google help.
As simple as that.

« Last Edit: 10/17/2023 03:39 pm by Emmettvonbrown »

#### Barley

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##### Re: Use of Metric Units
« Reply #63 on: 10/17/2023 04:07 pm »
By the way 'meter' should be spelt metre.
A meter is something you measure flow rate e.g. water meter.
Wrong.

SI standards do not specify spellings.  They even allow the use of alphabets that do not have some of the sounds needed to pronounce the units.

#### chopsticks

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##### Re: Use of Metric Units
« Reply #64 on: 10/17/2023 04:50 pm »
By the way 'meter' should be spelt metre.
A meter is something you measure flow rate e.g. water meter.
Wrong.

SI standards do not specify spellings.  They even allow the use of alphabets that do not have some of the sounds needed to pronounce the units.
Meh, they're not really wrong. It depends on the country and language. Here in Canada and in the UK the correct spelling is "re", so "meter" is not correct here (although many people do in fact spell it that way to to American influence).

The word metre comes from French, in which the spelling is, you guessed it: mètre.

It's linguistics and region.
« Last Edit: 10/17/2023 04:56 pm by chopsticks »

#### daedalus1

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##### Re: Use of Metric Units
« Reply #65 on: 10/17/2023 07:43 pm »
Barley, I explained what meter means in all the English speaking word. I didn't say it was wrong to spell metre for distance as meter, just that it is not good.

#### Walke Valentine

##### Re: Use of Metric Units
« Reply #66 on: 12/06/2023 01:07 pm »
I'm french and thus from the very country that created and then enforced the metric system. Yet, along the years (and with Google precious help, TBH) I worked my way through Imperial units.

1000 pounds is 454 kg.
2000 pounds, 908 kg.
That's the bare minimum for rocket payload conversions.

I do know that 37°C is 102°F because in high school I LMAO trying to imagine a person with a 102°C fever - that person would boil itself from the inside.

1 miles = 1.609 km, and that one is a huge PITA.

Feet are slightly better: 30.5 cm. Orbital velocity is 30 000 feet (aproximately).

I learned about inch to cm conversion (2.54) thanks to the NRO spysat mirrors. KH-8, KH-10, KH-11: 44 inch, 72-inch, 94 inch, and also rocket diameters.

As far as rocket diameters are concerned, 10 ft is close enough from 3 m (3.05 exactly) and the number in inch is not too tedious: 120 inch, Hubble mirror diameter before 1975 and Congressman Bolland, that idiot.

Worst thing is Machs to km/h to mph conversions - that's complete Hell on Earth.

I'm a German living in US for 5 years already. Still have some troubles with conversions. This site helps: https://oneconvert.com/unit-converters.
« Last Edit: 01/08/2024 01:32 pm by Walke Valentine »

#### eeergo

##### Re: Use of Metric Units
« Reply #67 on: 12/06/2023 01:32 pm »
I'm french and thus from the very country that created and then enforced the metric system. Yet, along the years (and with Google precious help, TBH) I worked my way through Imperial units.

1000 pounds is 454 kg.
2000 pounds, 908 kg.
That's the bare minimum for rocket payload conversions.

I do know that 37°C is 102°F because in high school I LMAO trying to imagine a person with a 102°C fever - that person would boil itself from the inside.

1 miles = 1.609 km, and that one is a huge PITA.

Feet are slightly better: 30.5 cm. Orbital velocity is 30 000 feet (aproximately).

I learned about inch to cm conversion (2.54) thanks to the NRO spysat mirrors. KH-8, KH-10, KH-11: 44 inch, 72-inch, 94 inch, and also rocket diameters.

As far as rocket diameters are concerned, 10 ft is close enough from 3 m (3.05 exactly) and the number in inch is not too tedious: 120 inch, Hubble mirror diameter before 1975 and Congressman Bolland, that idiot.

Worst thing is Machs to km/h to mph conversions - that's complete Hell on Earth.
I always remember that the speed of light is 300,000 km/s and is 186,000 mi/s.  From there you can easily convert miles and kilometers.

Being an experimental physicist by education, I find it tremendously useful to have learned through my American PhD advisor that a foot is roughly the distance electromagnetic waves (i.e. light) travels in a vacuum during a nanosecond, that is:

1 ft ≅ 1 l-ns
0.9836 ft = 1 l-ns, actually

In other words, light travels roughly a (short) billion ft/s. Uncanny! Hope that helps to tend bridges between both worlds. Not really fit to be used in your backyard, but people these days build the craziest things in their garages...
-DaviD-

#### Hobbes-22

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##### Re: Use of Metric Units
« Reply #68 on: 12/06/2023 02:26 pm »
I'm french and thus from the very country that created and then enforced the metric system. Yet, along the years (and with Google precious help, TBH) I worked my way through Imperial units.

1000 pounds is 454 kg.
2000 pounds, 908 kg.
That's the bare minimum for rocket payload conversions.

I do know that 37°C is 102°F because in high school I LMAO trying to imagine a person with a 102°C fever - that person would boil itself from the inside.

1 miles = 1.609 km, and that one is a huge PITA.

Feet are slightly better: 30.5 cm. Orbital velocity is 30 000 feet (aproximately).

I learned about inch to cm conversion (2.54) thanks to the NRO spysat mirrors. KH-8, KH-10, KH-11: 44 inch, 72-inch, 94 inch, and also rocket diameters.

As far as rocket diameters are concerned, 10 ft is close enough from 3 m (3.05 exactly) and the number in inch is not too tedious: 120 inch, Hubble mirror diameter before 1975 and Congressman Bolland, that idiot.

Worst thing is Machs to km/h to mph conversions - that's complete Hell on Earth.

useful approximate conversions:
Pounds to kg: divide by 2.2. So divide by 2, take the result, move the decimal point one position and subtract that.
1000 pounds: 500 - 50 = 450 kg. Close enough.

Km to mile: Multiply by 1.6. 50 miles is 80 km.
Foot to meter: divide by 3.
Fahrenheit to C: forget it, use a calculator.

#### Steve G

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##### Re: Use of Metric Units
« Reply #69 on: 12/06/2023 02:34 pm »
I'm Canadian and we went metric in the 1970s. But, if you ask anyone their weight and height, it's still in pounds, feet, and inches.

#### DanClemmensen

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##### Re: Use of Metric Units
« Reply #70 on: 12/06/2023 07:01 pm »
Fahrenheit to C: forget it, use a calculator.
Fahrenheit to Celsius:
Today only, price cut: take \$32 off. But wait, there's more! Take half off!, (there is  a 10% handling fee on the result and then 1% tax on that
100 F:   100-32 =68.   68/2=34.      34 +3.4 = 37.4.    37.4+.374=37.774 C

Celsius to Fahrenheit:
10% discount when buying 2, but there is a \$32 handling fee.
40 C:    2*40=80.     discount of \$8, so 72    72+32=104.

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##### Re: Use of Metric Units
« Reply #71 on: 12/06/2023 07:11 pm »
Metric is more logical, more useful, more interchangeable, globally recognized, avoids costly misunderstands and the ongoing costs of conversion in business.  Literally the only reason not to metricize is to avoid wounding the national ego and xenophobic feelings of a stubborn few, which not only isn't a problem, it's a feature.

Put your economy fully on a scientific footing and humiliate culture-war troglodytes who consistently hold your society back out of paranoia.  Win-Win.
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#### Arb

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##### Re: Use of Metric Units
« Reply #72 on: 12/06/2023 07:27 pm »
From back when the UK was switching (most things) to metric, the basics:
- Two and a quarter pounds of jam weigh about a kilogram.
- A litre of water’s a pint and three-quarters.
- A metre measures three foot three, it’s longer than a yard you see.

#### gtae07

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##### Re: Use of Metric Units
« Reply #73 on: 12/06/2023 08:03 pm »
I would hazard a guess that the brutal competitiveness of the automotive industry drives economies of scale to the global level, forcing even American forms to adopt the world-standard system of units. Aerospace, in part because it's dominated by military and quasi-military organizations that are oblivious to cost (SLS being an on-point example), is under much less pressure.

There are many barriers to aerospace going to the "global level" for suppliers, but it's not lack of cost pressure (because there is plenty of that in aerospace)...  instead, the small production runs and very high entry requirements (for qualification, recordkeeping, traceability, etc) restrict the number of potential suppliers and make it fairly uncommon to have multiple suppliers for a given item.  That doesn't even get into the various export control requirements.

Meanwhile almost everything in the industry from fasteners, fittings, and hardware, to approved material/fastener allowables to standard stock sizes for tubing, sheet, etc. (not to mention all of the machinery and tooling that make them) are all in imperial units--even many of the part numbers!  You can do all your design and calculation in metric if you want but if you want any economy of scale for buying your aerospace-grade approved bolts, nuts, rivets, fittings, cables, tubes, sheetmetal, etc. they're all going to come in nice round inch sizing, at least for any US based company.  At that point you might as well just stick to the units all the stuff comes in...

#### catdlr

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##### Re: Use of Metric Units
« Reply #74 on: 12/06/2023 08:42 pm »
And, when you work at JPL you always use Metric in trajectory adjustment, or is it Imperial??

It happens to the best of us.

« Last Edit: 12/06/2023 08:46 pm by catdlr »
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#### EE Scott

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##### Re: Use of Metric Units
« Reply #75 on: 12/06/2023 08:54 pm »
I'm Canadian and we went metric in the 1970s. But, if you ask anyone their weight and height, it's still in pounds, feet, and inches.

I recently started listening to CBC Radio during the day and I'm always surprised when I hear pounds, feet, inches and miles still used occasionally. As an American growing up in the 70s, when there was a national push to switch to metric, I always just assumed it was a matter of a few years and the US would be metric too. Sadly, still waiting...
« Last Edit: 12/06/2023 08:55 pm by EE Scott »
Scott

#### spacenut

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##### Re: Use of Metric Units
« Reply #76 on: 12/06/2023 09:36 pm »
Being an American, most car mechanics like the metric system.  5mm is smaller than 12mm for wrenches.  They don't have to figure as much.  Is it 5/8" wrench or 9/16".  9/16" is smaller than 5/8".  So metric is simpler.

When I was working for a gas utility.  We used Metric for highway measurements.  The 1996 summer Olympics were in Atlanta, so they put km posts along the highways.  This confused a lot of older people if they had an accident calling in, "I am at mile post 117, when it was km117.  Confused the response people like police, fire, medical, and towing services.  After the olympics, we switched back to English.  The problem was they left the old mile posts up along the same routes.  If they had removed the mile posts, it wouldn't have been so confusing and would have been easier to make the conversions.

I read that in the early 20th century, the American senate voted to continue to use the English system over the metric by 1 vote.  Otherwise the conversion would have already been made.

#### Hog

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##### Re: Use of Metric Units
« Reply #77 on: 12/07/2023 12:06 am »
When I comes to Maple Syrup and Whiskey, I'll take the Imperial/Canadian gallon over the US gallon everytime.(4.456 litres in the Imp. gallon vs 3.785 litres American).

The "quarting" of the Metric Litre is complete BS.  The Litre is 1000ml, not 946ml.
Paul

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##### Re: Use of Metric Units
« Reply #78 on: 12/07/2023 01:56 am »
I like the way SpaceX does it. Uses 6 foot sheets of 4mm steel to build Starships. They should weigh them in grains.
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#### RDoc

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##### Re: Use of Metric Units
« Reply #79 on: 12/07/2023 02:37 am »
I like the way SpaceX does it. Uses 6 foot sheets of 4mm steel to build Starships. They should weigh them in grains.
I'm assuming all their fasteners are Whitworth standard (post war).

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