Author Topic: Precision  (Read 796 times)

alanp

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Precision
« on: November 16, 2018, 11:45:27 PM »
https://www.stuff.co.nz/science/108677277/The-definition-of-a-kilogram-is-officially-going-to-change

Possibly a very geeky thing, but I can't help but think of the reason behind the metric system.

This is all AFAIK. Google an authoritative source (ie, not me.)

The chief, burning reason for the metric system was to define a system of measurement that could be replicated, anywhere, *PRECISELY*, independant of existing golden standards. One standard for the inch was three barleycorns. Barleycorns grown where? Of what dryness? Jammed together how hard? You'd never calibrate a micrometer with this level of precision.

Quote: "The metre was originally defined in 1793 as one ten-millionth of the distance from the equator to the North Pole." This meant that, given a good cartographer, you could recreate the golden standard for one meter anywhere on Earth. (On Mars, or Venus, you'd be out of luck, admittedly.) This repeatable standard was the basis for the other metric measurements -- one litre is defined as the volume contained by 0.01x0.01x0.01 meters. One kilogram, in turn, was defined as the weight of one litre of pure water, at sea level, at four degrees celcius.

Precision is important to a degree that would make a medieval peasant accuse a modern engineer of idolatry. It's interesting to investigate, and I highly suggest you do.
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alanp

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Re: Precision
« Reply #1 on: November 16, 2018, 11:49:52 PM »
<a href="http://www.youtube.com/watch?v=gNRnrn5DE58" target="_blank">http://www.youtube.com/watch?v=gNRnrn5DE58</a>
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thesmokingman

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Re: Precision
« Reply #2 on: November 17, 2018, 02:47:48 PM »
having worked extensively with metric and imperial standards in my initial course of study (engineering), the main glaring difference for me was that metric makes the math easier. units scale by multiples of ten, unit conversion is cleaner, significant digits (precision) are easier to establish. add on top of that the problem that the imperial system gets twisted by the particular application you're working with ... SAE has standards for parts and tools, machining is usually done in decimal place inches instead of fractional base 2 (half, quarter, eighth, sixteenth, thirty second, sixty fourth), carpentry works on nominal dimensions rather than actual, weight vs liquid volume (ounces) ... a real black hole of precision problems
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EBK

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Re: Precision
« Reply #3 on: November 17, 2018, 03:01:53 PM »
Not affiliated with Oatey, makers of the world's best and most delicious* low tar solder paste. Ask for Oatey -- It's the juiciest!

*Solder paste is not food.  If ingested, seek medical help promptly.

somnif

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Re: Precision
« Reply #4 on: November 17, 2018, 03:59:30 PM »
And yet my British friends still talk about miles-per-gallon when describing their cars.

cajone5

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Re: Precision
« Reply #5 on: November 17, 2018, 04:16:20 PM »
I find metric is easier for math, but harder to understand... For example...

Can you conceptualize a pound?, a psi? a psf?  Likely.

But tell me what a kilonewton feels like.  Or a Pascal.  This convenient system of measurement

Then again... what the hell is a slug?

thesmokingman

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Re: Precision
« Reply #6 on: November 17, 2018, 05:38:42 PM »
or grains ... drachms ... firkins ... tuns (and all the fun fractions of a tun like butt or hogshead)
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mjg

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Re: Precision
« Reply #7 on: November 17, 2018, 08:27:28 PM »
I find metric is easier for math, but harder to understand... For example...

Can you conceptualize a pound?, a psi? a psf?  Likely.

But tell me what a kilonewton feels like.  Or a Pascal.  This convenient system of measurement

Then again... what the hell is a slug?

Is that just upbringing though?  I have no idea what a pound is.  I can easily conceptualise a kilogram, and a litre, and can vaguely judge how many metres away something is. 

I have no idea how many miles per gallon my car gets, but I do know how many litres per 100km it uses. 

It was years of wondering what an oz was before someone told me it's pronounced 'ounces'.   ;D

alanp

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Re: Precision
« Reply #8 on: November 17, 2018, 08:32:37 PM »
Heh, the only things you buy in ounces here, are bought at the local tinnie house, most likely from either the Mongrel Mob, Black Power, Headhunters, or some other outfit.
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Muadzin

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Re: Precision
« Reply #9 on: November 18, 2018, 01:37:27 PM »
I find metric is easier for math, but harder to understand... For example...

Can you conceptualize a pound?, a psi? a psf?  Likely.

But tell me what a kilonewton feels like.  Or a Pascal.  This convenient system of measurement

Then again... what the hell is a slug?

Is that just upbringing though?  I have no idea what a pound is.  I can easily conceptualise a kilogram, and a litre, and can vaguely judge how many metres away something is. 

I have no idea how many miles per gallon my car gets, but I do know how many litres per 100km it uses. 

It was years of wondering what an oz was before someone told me it's pronounced 'ounces'.   ;D

That! A thousand times that! Imperial measurements are so damn illogical if you are brought up with metric. And I reckon its worse for us, because I get the impression that in the US and UK you at least are taught and use some metric in addition to imperial, whereas us Continental heathens are taught only metric. Some things are in imperial for some odd reason, probably because they were invented in the US or UK. TV screens are measured in inches, but I reckon that means little to us other then a bigger number in inches = a bigger screen. And bigger is always better. And feets seem to be still used in aviation. And those crazy mariners love their non-metric nautical terms.

ahiddentableau

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Re: Precision
« Reply #10 on: November 18, 2018, 05:33:54 PM »
I find metric is easier for math, but harder to understand... For example...

Can you conceptualize a pound?, a psi? a psf?  Likely.

But tell me what a kilonewton feels like.  Or a Pascal.  This convenient system of measurement

Then again... what the hell is a slug?

Is that just upbringing though?  I have no idea what a pound is.  I can easily conceptualise a kilogram, and a litre, and can vaguely judge how many metres away something is. 

I have no idea how many miles per gallon my car gets, but I do know how many litres per 100km it uses. 

It was years of wondering what an oz was before someone told me it's pronounced 'ounces'.   ;D

That! A thousand times that! Imperial measurements are so damn illogical if you are brought up with metric. And I reckon its worse for us, because I get the impression that in the US and UK you at least are taught and use some metric in addition to imperial, whereas us Continental heathens are taught only metric. Some things are in imperial for some odd reason, probably because they were invented in the US or UK. TV screens are measured in inches, but I reckon that means little to us other then a bigger number in inches = a bigger screen. And bigger is always better. And feets seem to be still used in aviation. And those crazy mariners love their non-metric nautical terms.

I can't speak for the UK, but my impression is that it's pretty close to the same as in Canada.  When you go to school here you're taught metric just about exclusively, but the culture and (for us, especially) our close proximity to America and American culture means you end up picking up both.  I'm basically equally comfortable in both worlds for this reason.  The result is that you end up using metric in some contexts and imperial in others.  In construction, for instance, it's really common to use imperial.  Commercial, or even at home woodworking, you're probably doing everything in imperial (on tools made for the US market).  But I don't buy any idea that imperial is somehow easier to conceptualize.  I agree that nobody can conceptualize a newton, but we don't ever talk about force.  So that's just based on what you use enough to get a firm hold of. 

somnif

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Re: Precision
« Reply #11 on: November 18, 2018, 05:41:12 PM »
A Newton is actually really easy to conceptualize.

Its the weight of an apple, give or take a bit.

An apple is about 1/10th a kilogram, and gravity is about 10m/s2, so it comes out to about 1N.