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  #61  
Old 10-13-2009, 08:33 AM
Robski Robski is offline
 
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Default

I'll apologise in advance for writing this as I read through the thread!

Quote:
Originally Posted by N999BT View Post
I am a mechanical engineer...

Oh. The one thing that does make some sense is nautical miles, since it actually relates to something on the ground, the distance between the equator and the pole, divided by 60 degrees, divided by 60 minutes, and actually appears on the vertical longitude lines on the maps we use.
And I have a degree in geography not that it helps much with business software development. I'd just like to say that Nautical miles are a great idea until you realise that the basis for the measurement is actually a variable.
The earth is not a perfect sphere: it is slightly flattened at the poles (technically an ellipsoid revolution).
A nautical mile was originally measured off the latitude scale on a chart: 1 minute of latitude = 1 nautical mile.
This means that nautical miles as measured on a maritime chart are shorter towards the poles than at the equator (I think I've got that the right way round, but you get the idea...).

Oh man, I carry some useless information around in my head!

Anyway, if you want a really stupid example of inconsistency, in the UK in air law (and aviation weather forecasts etc) all the defined horizontal distances are in metres, but all the vertical ones are in feet. Now explain to me how that's logical!

And don't get me started on Pints and Gallons. The US has it just plain wrong at 16 fluid ounces! A pint is 20 fluid ounces, same as a proper sized beer (even in the US). OK the US gallon is still 8 pints, but the damage has already been done by then!
I've never worked out why in the US, where everything is BIGGER, that the pint is smaller!

But then again, what do I know? My ASI main scale is in MPH but my GPS gives me ground speed in Knots. And yes, I installed the ASI, and I do know how to change the scales on the GPS - I just choose not to!

As for the Jag having different threads each end of a hose, sounds like the global multi-national Ford has been at work sourcing bits from it's cheapest subsidiaries. The British Morris Motor company used to do the same in the 1930's - the small engines were French so had metric threads but the nut and bolt heads were British Standard sizes as that's the sizes of the spanners all the garages that would have to repair them had. Flippin' confusing to work on until it's explained to you.
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  #62  
Old 11-28-2009, 08:41 AM
nucleus nucleus is offline
 
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Talking There is a certain elegance

to a system that is where it is all base ten based. So to speak. I also find elegance in the fact that the volume, weight and length units are all based on a cc of water... 1 gm H20=1 cc volume. I have never been able to remember the whole cups, ounces, pints, gallons thing.

Hans
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  #63  
Old 11-28-2009, 09:35 AM
Daver Daver is offline
 
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Default mixed units

I have never seen such a mixed up set of units until I entered this aviation thing.

Tradition over logic is my best explanation.

Its just a matter of getting used to it I guess.

I learned to love the metric (MKS) system of units in engineering school.

Always hated to get problems in other units: what the heck is "KIP" or a why
the same unit (LBS) for weight and mass, etc.,?

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  #64  
Old 11-28-2009, 12:33 PM
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shuttle shuttle is offline
 
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There was a comedian on BBC TV here in the UK the other evening joking about how the British use degrees F when talking about hot summer's days ("It will be in the 90's tomorrow!", doesn't happen very often here by the way) but use degrees C when talking about cold weather ("It was chilly today, -1 C").

Funny thing is that it's exactly what we do here, biggest numbers for hot, smallest for cold (though not on the TAFs/METARS!).
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  #65  
Old 11-28-2009, 09:32 PM
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fodrv7 fodrv7 is offline
 
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Default Metre not meter.

What a fabulous post.
Good bits of humour, lots of sarcasm and some seriously useful information. And so far no brawls; even though someone mention ?taildraggers.?

Let me get my ?units beef? out of the way first, because this will be a long post and nobody will bother to read to the end.
Choose! Metric or Imperial? But don?t ever have a rivet that is 3.5 of 3/32 long. How dumb to mix decimals and fractions in the one mouthful.
OK! Got that out of the way.

Now let?s get this straight. The USA has officially been Metric for over one hundred years since Grover was the boss.
In 1875, the United States solidified its commitment to the development of the internationally recognized metric system by becoming one of the original seventeen signatory nations to the Metric Convention.
Don?t believe me. Google ?Metrication in the United States wiki?.
I was bought up in Australia in the late 16th century when we used Imperial bits.
Whilst I was at college, Australia change to Metric.
So I?m ambidextrous and I know most Americans would give their right arm to be ambidextrous. Particularly if they were working on the Mars Orbiter.

And the use of 60 seconds is no more arbitrary (as someone suggested) than 16oz in a pint of US beer. (Poms feel cheated. They want 20oz of warm, flat, liquid amber). There are 60 seconds in an hour because the Babylonians used a sexagesimal (Base 60) system. And they invented the Rolex; or something similar. So they have a patent time.

There are a lot of comments in this post stating that some unit is arbitrary. No units are arbitrary. They relate to the ?Kings? Foot?, the ?Pharaoh's Arm? or something. They might seem antiquated, but they were chosen for a reason.

Sure, the metric System has some drawbacks, (it was invented by Man) most notably because we have ten digits on our hands. Eight would have made for a much better system. Dividing by two would be easy.

Certainly, conversion between Fahrenheit and Celcius would be easier if they had the same zero point, (ie. Zero at the freezing point of water) so that a simple rule of thumb could be used without having to account for the 32? offset. This is because Daniel Gabriel Fahrenheit did not use the same zero datum point as the Celsius scale uses, that is freezing water, instead using a frigorific Brine mixture which occurs at 32?F below the freezing point of water.

As someone pointed out knots, come from sailors who through a log overboard with a knotted rope attached and counted the knots paying out to estimate their speed. They wrote the result in a ?Logbook?. So if you don?t use knots you should be using an accountants ledger or a scrap of paper. But not a logbook.

Another post wondered why to the ?one-in-sixty rule? ,1:60 (60:1?) rule works.
It works because the Tan of a small angle is equal to 1/60th of the angle.

The problem is not so much that the Metric system or the Imperial system is superior, but rather that the Metric System has been adopted in the US by the Army, university and countless other organisations and not by the country as a whole.

Finally here is a map showing all the other developed countries in the World that DON?T use the Metric system.

Pete.

http://img69.imageshack.us/img69/994/metricmap.gif
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  #66  
Old 11-29-2009, 12:03 AM
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rv8ch rv8ch is online now
 
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Default more rules of thumb

Here is a metric cheat sheet - attention - there are "bad words" in the comic. http://xkcd.com/526/
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  #67  
Old 11-29-2009, 04:38 AM
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plehrke plehrke is offline
 
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Default It's is only units

First, lots of great posts in this thread.

With the world market place we have now and the mix of unit we have (as have been pointed out in this thread) it is a wonder we have not read about any incidents/accidents/screw-ups/emergencies due to mis-calculation of number conversion. The only one I know of was a Mars landers (built by Lockheed) that crashed into the planet due to the people working the hardware and those doing the flight software where using different units.

(How do they do it in Star Trek when the Romulains give Jean-Luc 24 hours to leave the neutral zone, what planet's rotational cycle is that hour based on?)
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  #68  
Old 11-29-2009, 05:47 AM
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Kevin Horton Kevin Horton is offline
 
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Quote:
Originally Posted by plehrke View Post
the world market place we have now and the mix of unit we have (as have been pointed out in this thread) it is a wonder we have not read about any incidents/accidents/screw-ups/emergencies due to mis-calculation of number conversion. The only one I know of was a Mars landers (built by Lockheed) that crashed into the planet due to the people working the hardware and those doing the flight software where using different units.
The Air Canada 767 "Gimli Glider" accident was triggered by a metric conversion screwup when refueling an aircraft with an unserviceable fuel indication system. The details of exactly how they screwed it up are in the "Refueling" of the wikipedia article.
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  #69  
Old 11-29-2009, 11:42 AM
Pilottonny Pilottonny is offline
 
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Default Maybe.....

Quote:
Originally Posted by fodrv7 View Post
..................Finally here is a map showing all the other developed countries in the World that DON?T use the Metric system.

Pete.

http://img69.imageshack.us/img69/994/metricmap.gif
those two countries are owned by the USA?
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  #70  
Old 11-29-2009, 02:11 PM
TThurston TThurston is offline
 
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Default People-centric units of measurement

I didn't read every post, so this may already have been mentioned. I do a lot of long distance walking, so I find it nice that a mile is a nice power of ten. If I count paces (every time I step with my left foot), I count to 1000, and I've walked a mile. After all, that's where the word for mile comes from, the latin for 1000.

Many statute measurements are based on people sized units (feet, miles, furlongs, degrees fahrenheit, etc). Metric units are not quite so people-centric, being based on concepts like the size of the earth, or some decimal fraction of that size, or a weight or volume of a standard substance related to a fraction of that size. I suppose nautical miles are similar to metric units, in being related to the size of the earth.

The point is, different measurement systems make more or less sense depending on whether they are used in the context in which they were originally defined, or in some context that is farther afield. For walking, miles makes sense to me.
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