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Thread: English/metric measurement error in the Mars Climate Orbiter

1. I could not agree more.

2. The Following User Says Thank You to Tonyg For This Useful Post:

mklotz (04-14-2019)

3. ¨Eleven inches to a foot!¨

Not only that. The feet and inches themselves might have been different. No worse than different gallon sizes plus several different types of ounces in both Canada and US. Inferial indeed. Hopeless.

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mklotz (04-14-2019)

5. American measurement standards are a rare issue where people are screaming for more government regulation. But they won't do it.

The catastrophic measurement confusion incidents certainly make the news. But we never hear about all of the other issues that resulted in lost productivity.

6. <<Instead of taking on the 20,088 litres of additional fuel that they required, they instead took on only 4,917 litres. The use of the incorrect conversion factor led to a total fuel load of only 22,300 pounds (10,100 kg) rather than the 22,300 kilograms that was needed.>>

This makes no sense. the volume ratio is 20088/4917 = 4.1 but the mass ratio is 2.2
Therefore if 20088 l is what was needed then a mass units error would mean that they took on 20088/2.2 = 9130 l not 4917.
The ratio of imperial gallon to litres is 4.54 and the US gallon to litres is 3.79, the quoted volume ratio of 4.1 sits neatly between these two so it is much more likely that it was a gallons to litres error rather than a lbs to kg issue. Maybe a mid-Atlantic conversion factor was used.

7. Originally Posted by Jon
American measurement standards are a rare issue where people are screaming for more government regulation. But they won't do it.

The catastrophic measurement confusion incidents certainly make the news. But we never hear about all of the other issues that resulted in lost productivity.
The use of different measurement systems creates more than enough errors but it is the way in which the imperial system is commonly misused that is responsible for arguably more mistakes.

In the metric system in any technical sphere it is almost universal to use kg for mass and newtons for force. In which case F=ma and a=F/m. Easy, simple, consistent and correct. It will only be supermarkets and similar establishments that use kg for both.

Users of the imperial system most often use lb and lbf for mass and force. Which is not a consistent pair of units. In which case F=ma/g and a=Fg/m. So practicioners of this nonsense are always faced with the question of "do I need to add g, if so is it part of the numerator or denominator"? Many errors have been caused by this confusion. This is not a problem of the imperial system (much though I hate it) rather it is a problem of MISUSE of the system. Used correctly lb is the unit of mass and the poundal is the correct and consistent unit of force. I do not recall ever seeing engineering calculations that used the poundal as they should.
In the aircraft industry it is common to use lbf for force and slugs for mass. At least these units are consistent and F=ma and a=F/m.

I recently saw an engineering professor from an American university use units which he called weight density. WHAT? To use the famous words of John McEnroe "YOU CAN NOT BE SERIOUS".
Density is defined as mass/volume. Using weight(force)/volume requires the use of g again. No wonder errors are made when students are subject to such error prone idiocy.

Rant over for now, but you never know when the button will be pressed again.

PS. for those unfamiliar with poundals and slugs.
1 lbf = 32.17 poundals
1 slug = 32.17 lb.

8. The Following 2 Users Say Thank You to tonyfoale For This Useful Post:

Jon (04-10-2019), MeJasonT (04-14-2019)

9. Drew,
It would be better if the rest of the world adopted Imperial measurements.
Speaking as an Englishman who uses both, Is it not more accurate to have a measurement with increments of a thou than a rounding of to a fraction of a mm.
I guess it depends on which you use as to weather you think its more accurate - they are both accurate if used properly. But still something i've often pondered knowing damn well it made no bloody difference. The good news is the vast majority of machine tools and feed/speeds are still in Imperial measurements.

There was a guy over here in Newcastle UK who kept selling in pounds to his customers and the council took him to court for breaches in wights and measures, they hounded the poor guy - He unfortunately committed suicide as a result of the burden of court costs and loss of business as a result of being shut down.

Funny how you can still buy a pint of beer or milk and road signs and car speed's are still in MPH. One day someone will get a medal off the queen for switching to use both measurements as an indication of our multi national trade. Who ever said the EU were controlling ?

10. I can remember going to Cheltnam with my stick to measure a horse so all of us in the North knew how big 13 hands was. lol. but that's what they did.
Again horses are still measured in Hands not mm. Someone has a lot to answer for. They haven't even finished the conversion to Metric yet - some 40+ years.
is 40 years not an imperial time scale should it not be in Kmh with regards to light years or speed of light such as in the transmission of light through fibre optics and even time itself as fibre optics/laser are now used to make the clock in Grenwich London more accurate.

https://www.rmg.co.uk/discover/behin...reenwich-laser

11. Originally Posted by Drew1966
It really would be so much safer if the few remaining countries would join the rest of the world in using the metric system.
Under Clinton the US was about to go metric but he decided that it would damage the economy at that time, meanwhile to follow in the Clinton US metrication policy Canada went ahead but that B4 Clinton backed off.

THe intent was to make US products more acceptable to the EU and Asian markets thus improving trade balances.

Consequently Canada lives with a crossover system.
Food products sport \$/kilo as well as \$/lb etc.
We don't do MPG but liters per 100 KMS
Getting correct 2 cycle oil/gas mixtures is a nightmare.
Building materials is another Zoo, studs etc are still in inch/foot but other products are totally metric.
Sheeting remains 4 x 8 with roofing tiles now metric.

The only metric change I liked was calculating for stair risers.

12. So which imperial system should we use then? English or American?

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12bolts (04-15-2019), MeJasonT (04-15-2019)

14. Originally Posted by Drew1966
So which imperial system should we use then? English or American?
For maximum confusion, both. And while you're at it, do all your calculations using Roman numerals and Egyptian fractions.

15. The Following 5 Users Say Thank You to mklotz For This Useful Post:

Drew1966 (04-14-2019), MeJasonT (04-15-2019), tonyfoale (04-15-2019), Tonyg (04-14-2019), Toolmaker51 (04-14-2019)

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