Metric & Imperial measurements

[gordonthemoron]

si units are all metric, they are used internationally, including in the US and UK:

SI Units

 

[dan_atki]

Best I could come up with in response to this speed test:

100/250 = 0.4 (that was a relatively easy mental calculation compared to what's coming!).

So in metric, this is 0.4m = 40cm = 400mm whichever you wish to use (m is the SI unit, cm is the most convenient for this measurement, mm shows a degree of accuracy).

In imperial this becomes 0.4 yards. Hmmmm. Well there are 36 inches in a yard, 0.4*36 was calculated to be 14.4 (4*3.6 - admittedly helped by using a base 10 system!). Only AFAIK imperial measurements never used decimals in their prime, but fractions. So this becomes 14 2/5 inches.

And admittedly, the imperial calculation was more difficult than the metric!

 

[mumrar]

Best I could come up with in response to this speed test:

100/250 = 0.4 (that was a relatively easy mental calculation compared to what's coming!).

So in metric, this is 0.4m = 40cm = 400mm whichever you wish to use (m is the SI unit, cm is the most convenient for this measurement, mm shows a degree of accuracy).

In imperial this becomes 0.4 yards. Hmmmm. Well there are 36 inches in a yard, 0.4*36 was calculated to be 14.4 (4*3.6 - admittedly helped by using a base 10 system!). Only AFAIK imperial measurements never used decimals in their prime, but fractions. So this becomes 14 2/5 inches.

And admittedly, the imperial calculation was more difficult than the metric!

Both answers are correct and I'm sure you appreciate the speed difference, the imperial would of course be expressed as 1ft 2 and 2/5ths inches. Nice and easy then

 

[Muttley]

It`ll never be expressed as 2/5ths.
It`d be 4/10ths.

Rounding down is a metric notion.

 

[mumrar]

It`ll never be expressed as 2/5ths.
It`d be 4/10ths.

Rounding down is a metric notion.

And therein lies the problem. No one would dispute the use of either metric measure, but not everyone knows the bizarre conventions of imperial.

 

[dan_atki]

It`ll never be expressed as 2/5ths.
It`d be 4/10ths.

Rounding down is a metric notion.

I'm going to have to disagree with you there.

I've just looked at the 1955 Fowler's Mechanics and Machinists Pocket Book that has been passed down through the family to me. In all of the tables it includes it has fractions expressed in their lowest form (mathematically speaking, this isn't the same as rounding down ).

Taking one such table (Weight of one foot of square iron) it has the following 'side of square (inches)' in one of its columns:
11/16, 3/4, 13/16, 7/8, 15/16, 1, 1 1/16, 1 1/8, 1 3/16, 1 1/4, 1 5/16, 1 3/8, 1 7/16, 1 1/2

each one being the previous + 1/16 and simplified to its lowest mixed form. So the concept was around in 1955 when we were still under the grips of imperial (shown by the mass use of inches and pounds throughout the book!).

 

[thelem]

People here still think that 9/11 is the 9th of November. It should be written as 31/12/2009 not 12/31/2009.

Don't get me started on the stupid american dates! I had a spreadsheet "helpfully" autocomplete "May 08" into "05/08/2009". I meant May 2008 you silly thing!
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Both answers are correct and I'm sure you appreciate the speed difference, the imperial would of course be expressed as 1ft 2 and 2/5ths inches. Nice and easy then

Don't you have to use a base 2 number as the divisor, so
1ft 2 and 6/16th inches (approx)

 

[dan_atki]

Don't you have to use a base 2 number as the divisor, so 1ft 2 and 6/16th inches (approx)

I think you're making a valid point there based on looking through the above book. So accuracy is lost too as there is no such n that 2^n is a multiple of 5...

Metric is certainly more useful here!

 

[thelem]

Accuracy isn't really an argument for either system, because both can be as accurate as each other, and both are able to precisely specify quantities that they other can only approximate.

The imperial system is actually more flexible with accuracy, because each time you make it more accurate you make it two times more accurate (once you get down to the smallest unit), where as in metric you have to go to ten times more accurate.

How do you specify the accuracy using imperial though? In metric, I might say that 1234ml was 1200ml or 1.2L to 2s.f. (significant figures). Do I say 1ft 2 and 6/16th to the nearest 16th of an inch? I'm assuming that we'd simplify 12/32nd down to 6/16th, so you can't just look at the divisor (i.e. the 16 or 32 in my examples.)

 

[O L Leigh]

it makes no sense for computers to store imperial units as they work in base 10 (although the data may be store in base 2, 8 or 16).

No they don't. They work in binary, which is actually closer to the imperial system than metric. This is why you have 16, 32, 64 or 128 bit encryption rather than 10 or 100 bit encryption, for example.

Quite honestly I can't get excited about this subject. Whether the distance from an AWS magnet to the signal is expressed as 200 yards or 183 metres really makes no difference to the way I drive. However, even now the locations of things like Emergency Speed Restrictions are still stated in miles and chains. We still have mileposts every quarter of a mile. The only place where you will see any evidence of the metric taking over from the imperial is on recently erected OLE structures in the form of the structure numbers.

The only place I like the old imperial measurements is on road signs. I have a good idea of how far 20 miles is but would struggle to comprehend 20 kilometres.

O L Leigh