Units of measurement

Besoeker

Senior Member
Location
UK
The word metric is for measurement, not specifically length. I always assumed the meter comes from the metric system, not vice versa. Yes, it's the modern International System, or SI, also, but it's not wrong to call it the metric system. EVERYONE knows what it means.

When we talk about the metrics of a baseball pitcher, or anything, we aren't referring to measurements of length usually.
Definition of metric - relating to or based on the metre as a unit of length, relating to or denoting a metric.
English Oxford Dictionary.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
There are multiple issues here.

SI is convenient because it is a self consistent system of units. When physics relates two properties, the units are related so that you don't need conversion factors or 'constants' to make the equations work out.

In SI you can answer F=MA without having to somehow work in '32 feet per second per second' or other similar nonsense.

But the objection to the _particular_ units selected remains, and the selection was in many ways political.

Much of the 'forced metrification' uses units that are only vaguely related to SI...places switching from miles per hour to kilometers per hour as if this were meaningful. Pressure gauges with 'kg/cm^2' on them as if this were even a real unit of pressure. It makes me want to scream and start using dodecimeters and heptagrams.

Between Celsius and Fahrenheit, Fahrenheit makes more sense for _human_ temperature measurements...and if you want to do science it makes more sense to use an absolute temperature scale. Celsius is not part of SI, and enforced metrification to use Celsius is just silly. Use a temperature scale where the triple point of water is 500 units on an absolute thermodynamic scale; then subtract 500 to get the 'human' version.

The selection of the length of the meter is historic, an itself no better than the foot...in fact I would argue that the unit of length should be 1/1000000000 the distance light travels in a second...which is just about 1 foot!

On things like wire gauge, AWG is kind of ugly, but an exponential scale makes sense. I'd prefer something where an integral number of gauge counts resulted in an _exact_ doubling of cross section, not the _approximate_ doubling gotten from 3 gauge counts in AWG.

It goes on. Self consistent units are good, but SI itself was not handed down on high as perfect.

-Jon
 

sameguy

Senior Member
Location
New York
Occupation
Master Elec./JW retired
Sure as soon as one of the other countries lands a man on the moon.
What will happen to all the sayings, give an inch take a mile?
 

Besoeker

Senior Member
Location
UK
There are multiple issues here.

SI is convenient because it is a self consistent system of units. When physics relates two properties, the units are related so that you don't need conversion factors or 'constants' to make the equations work out.

In SI you can answer F=MA without having to somehow work in '32 feet per second per second' or other similar nonsense.

But the objection to the _particular_ units selected remains, and the selection was in many ways political.

Much of the 'forced metrification' uses units that are only vaguely related to SI...places switching from miles per hour to kilometers per hour as if this were meaningful. Pressure gauges with 'kg/cm^2' on them as if this were even a real unit of pressure. It makes me want to scream and start using dodecimeters and heptagrams.

Between Celsius and Fahrenheit, Fahrenheit makes more sense for _human_ temperature measurements...and if you want to do science it makes more sense to use an absolute temperature scale. Celsius is not part of SI, and enforced metrification to use Celsius is just silly. Use a temperature scale where the triple point of water is 500 units on an absolute thermodynamic scale; then subtract 500 to get the 'human' version.

The selection of the length of the meter is historic, an itself no better than the foot...in fact I would argue that the unit of length should be 1/1000000000 the distance light travels in a second...which is just about 1 foot!

On things like wire gauge, AWG is kind of ugly, but an exponential scale makes sense. I'd prefer something where an integral number of gauge counts resulted in an _exact_ doubling of cross section, not the _approximate_ doubling gotten from 3 gauge counts in AWG.

It goes on. Self consistent units are good, but SI itself was not handed down on high as perfect.

-Jon
I don't think anyone would claim that it is perfect. It is just so much simpler.
 

Besoeker

Senior Member
Location
UK
And the Metric System is based on the meter... and the second, and the lumen...

The definitions in the dictionary are more than just the one quoted.
I'll try this again. The metre is a unit of length. You can't measure a kilogram in metres.
It's SI.
 

Adamjamma

Senior Member
I will just say this... when buying cement I think in terms of feet, square feet , yards, square yards, cubic feet, cubic yards, and tons. I cannot think of it in meters, or cubic meters... I have tried, but cannot. Yet, I have no problems in rough figuring rooms at 2.44 meters in height, counters as being 50 pr 60 cm wide, etc..,
i actually prefer using combinations of feet and meters when measuring furniture in carpentry, etc, and most of my architectural drawings use both metric and imperial, in different colors... I actually own t bars and such in both formats, metal rulers in both formats, etc.
Because I have done work in so many areas, in so many formats, I don’t think about it too much. Rough carpentry I do in feet but when I try to make a dresser drawer or a fancy door, I switch to metric, and never think about it... I can get more accurate cuts by using metric, and it is easier for me to lay out a room in metric, given more and more tiles are set and sold in metric based sizes.
So, now I just need to find a way to put the NEC wire tables in my books using the metric wire sizes like used in Europe and Jamaica, and then also do the conduit tables the same way... because unfortunately for me, suppliers in Jamaica get whatever supplies they can get, and have a take it or leave it attitude so one can start a project with US conduits, outlet boxes, and wire, halfway through the project only find Canadian parts, and suddenly the only wire available is European... unless one wants to wait for a few months or pay for a special shipment... the joys of living in the third world.
So, knowledge of the correct conversions from 12 gauge to 2.5 or 4mm wire, or how many 12 gauge wires fit in a fifteen mm conduit compared to a 1/2 inch conduit... difference may not seem like much but there are differences.
 

MAC702

Senior Member
Location
Clark County, NV
I'll try this again. The metre is a unit of length. You can't measure a kilogram in metres.
It's SI.
Actually, yes; yes you do. The kilogram is based on the mass of one liter of water. One liter is the volume of 0.1 x 0.1 x 0.1 meters. It's done that way on purpose. It's the Metric System. It's no big deal that it is. The Metric System is also adopted internationally, and known as the International System.

Definition 1 is what you are adamantly adhering to. Definition 1.1 also applies quite well, especially in our vernacular.

https://en.oxforddictionaries.com/definition/metric
 

Besoeker

Senior Member
Location
UK
Actually, yes; yes you do. The kilogram is based on the mass of one liter of water. One liter is the volume of 0.1 x 0.1 x 0.1 meters. It's done that way on purpose. It's the Metric System. It's no big deal that it is. The Metric System is also adopted internationally, and known as the International System.

Definition 1 is what you are adamantly adhering to. Definition 1.1 also applies quite well, especially in our vernacular.

https://en.oxforddictionaries.com/definition/metric
Two different SI physical units. That they can be related in that way doesn't make them the same.
The relationship further goes to show the elegant simplicity of SI.
Embrace it...........:D
 

kwired

Electron manager
Location
NE Nebraska
We have a lot of SI units being the standard to use here, but it varies from one trade/industry to another, and some trades/industries like to mix it up. Automobiles, a lot of dimensional items are standardized on SI units. We often put in gallons of fuel, quarts of oil, etc. Speed is usually miles per hour.

Medical, pharmaceutical and related professions - nearly everything is done with SI units.

Retail, especially food and beverages - is a bit of a mixture as well. Items sold by weight seem to tend to be sold by ounce/pound. Items sold by volume seem to be common to be either way. Beverages in particular seem to sell same product in both ounces and in liter based units.
 
... For example, is there any sense in two different units for power? ...
Two? I'm aware of the watt, English horsepower, metric horsepower, boiler horsepower, refrigeration ton, BTU/hr, erg/s (the old metric system), donkey power, and pirate-ninja.

... Doesn't the UK still express fuel economy in miles per gallon? Or is that just Canada?
Canadian new-car fuel-economy window stickers express both fuel consumption in liters per hectokilometer, and fuel economy in miles per Imperial gallon.
(I'm a little embarrassed to admit how long it took me to figure out why Canadian cars achieved 20% better miles-per-gallon than their apparently-identical American counterparts)

Canadian road signs -- at least in Ontario -- seem to be exclusively in kilometers; fuel sales seem to be exclusively in liters; and speedometers seem to be exclusively in kilometers per hour.


I'm amused -- yes, I have a dark sense of humor -- by Americans who adamantly insist on using the British system because "everybody's familiar with it", but haven't a clue how big a pint is. And often, haven't a clue about the whole concept of measurement itself.


My pet peeve is the lack of consistency in counting the number of wires in a cable. 12/3 NM contains four wires, but 12/3 SO contains three.


Eventually, people will see the value of working in one consistent system of weights & measures, but "eventually" may be a long time. Real progress sometimes occurs only one funeral at a time.
 

myspark

Senior Member
Location
SCV Ca, USA
Occupation
Retired EE
Two? I'm aware of the watt, English horsepower, metric horsepower, boiler horsepower, refrigeration ton, BTU/hr, erg/s (the old metric system), donkey power, and pirate-ninja.


Canadian new-car fuel-economy window stickers express both fuel consumption in liters per hectokilometer, and fuel economy in miles per Imperial gallon.
(I'm a little embarrassed to admit how long it took me to figure out why Canadian cars achieved 20% better miles-per-gallon than their apparently-identical American counterparts)

Canadian road signs -- at least in Ontario -- seem to be exclusively in kilometers; fuel sales seem to be exclusively in liters; and speedometers seem to be exclusively in kilometers per hour.


I'm amused -- yes, I have a dark sense of humor -- by Americans who adamantly insist on using the British system because "everybody's familiar with it", but haven't a clue how big a pint is. And often, haven't a clue about the whole concept of measurement itself.


My pet peeve is the lack of consistency in counting the number of wires in a cable. 12/3 NM contains four wires, but 12/3 SO contains three.


Eventually, people will see the value of working in one consistent system of weights & measures, but "eventually" may be a long time. Real progress sometimes occurs only one funeral at a time.

A 125 million-dollar Mars Orbiter was lost in space due to different units of measure.
A group of Lockheed engineers used the English units as opposed to NASA standard of metric system.


This caused the Mars Orbiter to overshoot its planned orbit in Mars and is now probably orbiting the Sun which created its own orbit. :blink:



See how this happened:


http://www.cnn.com/TECH/space/9909/30/mars.metric.02/
 
Last edited:

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
A 125 million-dollar Mars Orbiter was lost in space due to different units of measure.
A group of Lockheed engineers used the English units as opposed to NASA standard of metric system.
When this loss was first reported to me, it was reported as a metric to SI conversion error. The person saying this had mis-spoken, however at the time I was immersed in things like the difference between dynes and Newtons, and actually believed it was an error caused by different teams using different 'metric' systems.

-Jon
 
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