Units Of Measure

[steve_bank]

Scale of temperature - Wikipedia

en.wikipedia.org

Celsius (known until 1948 as centigrade) is a temperature scale that is named after the Swedish astronomer Anders Celsius (1701–1744), who developed a similar temperature scale two years before his death. The degree Celsius (°C) can refer to a specific temperature on the Celsius scale as well as a unit to indicate a temperature interval (a difference between two temperatures).

From 1744 until 1954, 0 °C was defined as the freezing point of water and 100 °C was defined as the boiling point of water, both at a pressure of one standard atmosphere.[citation needed]

Although these defining correlations are commonly taught in schools today, by international agreement, between 1954 and 2019 the unit degree Celsius and the Celsius scale were defined by absolute zero and the triple point of VSMOW (specially prepared water). This definition also precisely related the Celsius scale to the Kelvin scale, which defines the SI base unit of thermodynamic temperature with symbol K. Absolute zero, the lowest temperature possible, is defined as being exactly 0 K and −273.15 °C. Until 19 May 2019, the temperature of the triple point of water was defined as exactly 273.16 K (0.01 °C). This means that a temperature difference of one degree Celsius and that of one kelvin are exactly the same.

On 20 May 2019, the kelvin was redefined so that its value is now determined by the definition of the Boltzmann constant rather than being defined by the triple point of VSMOW. This means that the triple point is now a measured value, not a defined value. The newly-defined exact value of the Boltzmann constant was selected so that the measured value of the VSMOW triple point is exactly the same as the older defined value to within the limits of accuracy of contemporary metrology. The degree Celsius remains exactly equal to the kelvin, and 0 K remains exactly −273.15 °C.

Triple point - Wikipedia

en.wikipedia.org

In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium.[1] It is that temperature and pressure at which the sublimation, fusion, and vaporisation curves meet. For example, the triple point of mercury occurs at a temperature of −38.8 °C (−37.8 °F) and a pressure of 0.165 mPa.

 

[Shadowy Man]

If I recall, a mile was based on 1000 paces of a Roman soldier. Mille-mile.
The first thing we did in surveying was know your pace. Very useful for finding old monuments.

was a “pace” one step or two?

 

[Bronzeage]

Precision is money. I wear a Casio wrist watch that costs about $12. An atomic clock(a real one) starts at around $3000, but I don't know if I would trust it for anything that actually needed an atomic clock. If the atomic clock and my Casio disagreed on the time, I would suppose the atomic clock was correct, but how would I actually know?

Precision is good to have, but the benefits of increased precision taper off pretty quickly for most purposes. I put more value on accuracy, which is to say, if I measure something to be 1 inch long with a micrometer, I hope it still measures an inch when I come back from lunch. Nobody wants a micrometer that disagrees with itself. I don't use a micrometer very often, but I probably take a couple hundred measurements a day. There are situations where the money invested in precision is wasted. In woodworking, there is no such thing as 1/64 of an inch and 1/32 of an inch is very rare. There's no point to a precise measurement, if you can use it. A piece of wood can be shorter or longer by 1/32 of an inch because the weather changed, or in my case, the air conditioner kicked on.

My drafting teacher(a primitive system of drawing precision plans with a pencil) said, "There's no reason to take the dimensions out to three decimal places when they are going to measure it with a stick, mark it with chalk, and cut it with an ax.

 

[robnisch]

If I recall, a mile was based on 1000 paces of a Roman soldier. Mille-mile.
The first thing we did in surveying was know your pace. Very useful for finding old monuments.

was a “pace” one step or two?

Good question. We walked back and forth on a 100' coarse and took an average. IIRC mine was @ 2.4'. 2.4X1000=2400'. 2.4X2X1000=4800'.
Mile= 5280'.

 

[bilby]

I praise Thailand as a holiday destination but -- Warning! -- when you first step outside you may be aghast at the heat. ("Airline? It's too hot here. Change my return ticket; I'm going home TODAY!")

I live in Brisbane. We do plenty of 35-40° humid days in summertime.

But I have more sense than to go out in it.

27° is too cold, and 28° too warm.

27°??? What are you, a lizard?

23° is comfortable. At 27° I would be melting down so badly that Jane Fonda would be making alarmist movies about me.

I thought of altering the numbers to avoid this predicted complaint.
But "Honesty is the best policy."

I'm not sure why 27° seems quite comfortable for me. Is it because the cool air is directed toward me? Is it because of the years I've spent in the Land of Smiles without A/C at all? Is it because I'm often half or wholly naked?

I do set the car's A/C to about 22° but that's almost irrelevant as I control the driver's coolness with other controls, especially fan speed.


ETA. In future I think you should show contrition for calling me a lizard by answering at least one of my questions, e.g.

It was a simple pleasure to split an English pound three ways in the olden days: Each drinker owes six shillings and eight-pence. Have you ever watched three American tourists try to split a 1 Euro bill in Europe?

I have had the pleasure of watching an American tourist in Australia completely lose his shit over being scammed by an icecream vendor.

His change came to $x.27, but he only got $x.25 back, and when he complained, the vendor explained that change is always rounded to the nearest 5¢.

Then it was on.

The vendor appealed, to no avail, that not only was it lawful to round down, but that it was actually physically impossible to tender 27¢ in Australia, because our smallest coin is 5¢.

Eventually the vendor gave him an extra 5¢, just to shut him up.

It didn't work. He's probably still complaining.

 

[bilby]

If I recall, a mile was based on 1000 paces of a Roman soldier. Mille-mile.
The first thing we did in surveying was know your pace. Very useful for finding old monuments.

was a “pace” one step or two?

Yes.

Is a step completed when your front leg has cycled to become your back leg, or when it has returned to its initial "front leg" position?

 

[bilby]

Precision is money. I wear a Casio wrist watch that costs about $12. An atomic clock(a real one) starts at around $3000, but I don't know if I would trust it for anything that actually needed an atomic clock. If the atomic clock and my Casio disagreed on the time, I would suppose the atomic clock was correct, but how would I actually know?

Precision is good to have, but the benefits of increased precision taper off pretty quickly for most purposes. I put more value on accuracy, which is to say, if I measure something to be 1 inch long with a micrometer, I hope it still measures an inch when I come back from lunch. Nobody wants a micrometer that disagrees with itself. I don't use a micrometer very often, but I probably take a couple hundred measurements a day. There are situations where the money invested in precision is wasted. In woodworking, there is no such thing as 1/64 of an inch and 1/32 of an inch is very rare. There's no point to a precise measurement, if you can use it. A piece of wood can be shorter or longer by 1/32 of an inch because the weather changed, or in my case, the air conditioner kicked on.

My drafting teacher(a primitive system of drawing precision plans with a pencil) said, "There's no reason to take the dimensions out to three decimal places when they are going to measure it with a stick, mark it with chalk, and cut it with an ax.

Our run-prints provide the total distance (in km) for a set of trips, so that the driver can check that he has sufficient fuel to do the run, and return to the yard.

The paper run prints give this information to six decimal places, but on the new electronic system, it's given to eight.

Given that the bus is 12.5m long, and might be returned to any one of twenty lanes, each 3m apart, and to any of the 5-8 bus length positions on those lanes, I question the value of measuring trips to the millimetre, much less to the nearest 10 microns.

I do wonder if they have to re-work the calculation for an entire set of runs whenever one of the buses gets washed, and shortens by a few micronns of dust and grime.

I also hesitate to calculate my fuel to such precise margins, just in case I accidentally stop a millimetre too far along the lane, and run out of gas.

 

[Swammerdami]

It was a simple pleasure to split an English pound three ways in the olden days: Each drinker owes six shillings and eight-pence. Have you ever watched three American tourists try to split a 1 Euro bill in Europe?

I have had the pleasure of watching an American tourist in Australia completely lose his shit over being scammed by an icecream vendor.

His change came to $x.27, but he only got $x.25 back, and when he complained, the vendor explained that change is always rounded to the nearest 5¢.

Then it was on.

The vendor appealed, to no avail, that not only was it lawful to round down, but that it was actually physically impossible to tender 27¢ in Australia, because our smallest coin is 5¢.

You don't have banking apps on your phones? I once transferred ฿0.01 to my daughter, just to verify that I could. That's equivalent to .03¢ US at the current exchange rate. (By .03¢ US I mean about one thirtieth part of a penny, NOT 3 cents as many or most Americans would read it.)

Americans are a thrifty people. A penny here, a penny there -- Before long it adds up to a nickel!

Or maybe the Yank hoped you Aussies still made pennies out of copper!

On the topic of precious metals, if that's not still a sore subject, the U.S. futures market now shows copper at almost 39¢ per troy ounce, or almost 2¢ per pennyweight. (The old American penny weighed almost 2 pennyweights.) AFAICT this is the highest price ever quoted for copper since Donny Grump the Caveman was enticing underage children with precious metal baubles back in the Stone Age. Was anyone here smart enough to jump on FCX when it was selling for $30 a share in April?
But be aware that the 39¢ per troy ounce price requires that you deliver the copper to the U.S.A. For some reason the free world price for copper is significantly lower (maybe €0.224 per troy ounce?):

Spoiler

U.S. President Donald Trump said on July 8 that he would announce a 50% tariff on copper imports, sending U.S. Comex copper futures up more than 12% to a record high.
Prices on the Shanghai Futures Exchange (SHFE) and London Metal Exchange (LME) fell in the aftermath as the announcement signalled an end to a months-long arbitrage trade that had drawn the metal from global markets.

Eventually the vendor gave him an extra 5¢, just to shut him up.

Only three cents extra for pain and suffering? What about psychiatric therapy?

 

[Tigers!]

It was a simple pleasure to split an English pound three ways in the olden days: Each drinker owes six shillings and eight-pence. Have you ever watched three American tourists try to split a 1 Euro bill in Europe?

Or watch 3 American tourists try to split a 3 dollar bill in Australia

 

[Loren Pechtel]

In woodworking, there is no such thing as 1/64 of an inch and 1/32 of an inch is very rare. There's no point to a precise measurement, if you can use it. A piece of wood can be shorter or longer by 1/32 of an inch because the weather changed, or in my case, the air conditioner kicked on.

I'm pretty sure my former boss cared about 1/32". It's a matter of consistency, not accuracy per se. The door guys and the frame guys are going to pick pieces from stock, they should fit together so as to not leave any gaps. And remember that the maximum deviation is twice as big as the accuracy. And the pieces from chopsaw #1 should work with the pieces from chopsaw #2.

 

[Tigers!]

I praise Thailand as a holiday destination but -- Warning! -- when you first step outside you may be aghast at the heat. ("Airline? It's too hot here. Change my return ticket; I'm going home TODAY!")

I live in Brisbane. We do plenty of 35-40° humid days in summertime.

You forgot to add the 'C' for our yank friends.

But I have more sense than to go out in it.

How can that be as you are a Pom (from Blighty)? (With apologies to Noel Coward)

27° is too cold, and 28° too warm.

27°??? What are you, a lizard?

23° is comfortable. At 27° I would be melting down so badly that Jane Fonda would be making alarmist movies about me.

I thought of altering the numbers to avoid this predicted complaint.
But "Honesty is the best policy."

I'm not sure why 27° seems quite comfortable for me. Is it because the cool air is directed toward me? Is it because of the years I've spent in the Land of Smiles without A/C at all? Is it because I'm often half or wholly naked?

I do set the car's A/C to about 22° but that's almost irrelevant as I control the driver's coolness with other controls, especially fan speed.


ETA. In future I think you should show contrition for calling me a lizard by answering at least one of my questions, e.g.

It was a simple pleasure to split an English pound three ways in the olden days: Each drinker owes six shillings and eight-pence. Have you ever watched three American tourists try to split a 1 Euro bill in Europe?

I have had the pleasure of watching an American tourist in Australia completely lose his shit over being scammed by an icecream vendor.

His change came to $x.27, but he only got $x.25 back, and when he complained, the vendor explained that change is always rounded to the nearest 5¢.

Then it was on.

The vendor appealed, to no avail, that not only was it lawful to round down, but that it was actually physically impossible to tender 27¢ in Australia, because our smallest coin is 5¢.

Eventually the vendor gave him an extra 5¢, just to shut him up.

It didn't work. He's probably still complaining.

 

[bilby]

But I have more sense than to go out in it.

How can that be as you are a Pom (from Blighty)? (With apologies to Noel Coward)

You don't keep a mad dog, and go out in the midday sun yourself...

 

[Bronzeage]

In woodworking, there is no such thing as 1/64 of an inch and 1/32 of an inch is very rare. There's no point to a precise measurement, if you can use it. A piece of wood can be shorter or longer by 1/32 of an inch because the weather changed, or in my case, the air conditioner kicked on.

I'm pretty sure my former boss cared about 1/32". It's a matter of consistency, not accuracy per se. The door guys and the frame guys are going to pick pieces from stock, they should fit together so as to not leave any gaps. And remember that the maximum deviation is twice as big as the accuracy. And the pieces from chopsaw #1 should work with the pieces from chopsaw #2.

Your boss was wasting time and money if he wanted pieces cut to 1/32 of an inch.

One thirtysecond of an inch might be a practical consideration if you are building a bookshelf on the Space Station, but sawdust would be a problem. Wood shrinks and expands constantly in reaction to the environment. A board can be cut to 96.000 inches and tomorrow it's going to be a little longer, maybe a little shorter, and definitely not the same width or thickness.

As I said above, precision is money. You want more precision, you have to spend more money. This is the cost of extra labor, more expensive machinery, and rejected pieces that don't meet specs. Zero defects implies infinite cost and that shoots the hell out of profits.

 

[bilby]

Zero defects implies infinite cost and that shoots the hell out of profits.

Which is how you kill nuclear power, even though it's fundamentally cheaper, safer, cleaner, and longer lived (both in terms of fuel supply and the working life of powerplants) than coal power.

 

[Loren Pechtel]

In woodworking, there is no such thing as 1/64 of an inch and 1/32 of an inch is very rare. There's no point to a precise measurement, if you can use it. A piece of wood can be shorter or longer by 1/32 of an inch because the weather changed, or in my case, the air conditioner kicked on.

I'm pretty sure my former boss cared about 1/32". It's a matter of consistency, not accuracy per se. The door guys and the frame guys are going to pick pieces from stock, they should fit together so as to not leave any gaps. And remember that the maximum deviation is twice as big as the accuracy. And the pieces from chopsaw #1 should work with the pieces from chopsaw #2.

Your boss was wasting time and money if he wanted pieces cut to 1/32 of an inch.

One thirtysecond of an inch might be a practical consideration if you are building a bookshelf on the Space Station, but sawdust would be a problem. Wood shrinks and expands constantly in reaction to the environment. A board can be cut to 96.000 inches and tomorrow it's going to be a little longer, maybe a little shorter, and definitely not the same width or thickness.

You're missing the point--consistency, not true accuracy. Environmental reactions will change all the parts, no problem.

As I said above, precision is money. You want more precision, you have to spend more money. This is the cost of extra labor, more expensive machinery, and rejected pieces that don't meet specs. Zero defects implies infinite cost and that shoots the hell out of profits.

The objective was that the chop saws would cut to the required precision. Most other companies cut them longer and trim to length, we were cutting directly to length. We weren't asking for more precision than normal, we were asking for the same precision in one cut instead of two. It worked--we were killing the competition but that didn't do any good when the housing collapse took out most of our business.

 

[steve_bank]

Accuracy is how close a measurement is to a true value.

In precision engineering the closer tolerance you want on a machined part the more expensive it is.

At some point parts are machined as close as possible, then parts are selected that are measured to meet the higher tolerances. The rest is scrap metal.

Wood or metal both change size with environmental conditions.

The min and max dimensions of a part including manufacturing and environmental changes arr found. Then the assembled assembly of multiple parts is toleranced..

The finest resolution I know of in general dimensional measurement is laser interferometry. For a HeNe laser max resolution can be on the order of 1/4 wavelength of red light.

I believe lumber mills use it for measuring lengths. It is a common technology in different forms. A laser gauge.

Mount a retro reflector on a rail. Zero out a counter at the zero position. Shine a laser beam at the reflector through a beam splitter. Some light is transmitted and some split to a detector. As the reflector moves the reflected wave phase shifts. When phase of reflected and transmitted light are out 180 degrees there is zero or a minimum of light at the detector. Count the number of extinctions.

Light from a collimated laser has high phase coherence from the laser. Phase of the light leaving the laser does not change phase enough over the measurement interval to affect measurement,.

 

[Bronzeage]

In woodworking, there is no such thing as 1/64 of an inch and 1/32 of an inch is very rare. There's no point to a precise measurement, if you can use it. A piece of wood can be shorter or longer by 1/32 of an inch because the weather changed, or in my case, the air conditioner kicked on.

I'm pretty sure my former boss cared about 1/32". It's a matter of consistency, not accuracy per se. The door guys and the frame guys are going to pick pieces from stock, they should fit together so as to not leave any gaps. And remember that the maximum deviation is twice as big as the accuracy. And the pieces from chopsaw #1 should work with the pieces from chopsaw #2.

Your boss was wasting time and money if he wanted pieces cut to 1/32 of an inch.

One thirtysecond of an inch might be a practical consideration if you are building a bookshelf on the Space Station, but sawdust would be a problem. Wood shrinks and expands constantly in reaction to the environment. A board can be cut to 96.000 inches and tomorrow it's going to be a little longer, maybe a little shorter, and definitely not the same width or thickness.

You're missing the point--consistency, not true accuracy. Environmental reactions will change all the parts, no problem.

As I said above, precision is money. You want more precision, you have to spend more money. This is the cost of extra labor, more expensive machinery, and rejected pieces that don't meet specs. Zero defects implies infinite cost and that shoots the hell out of profits.

The objective was that the chop saws would cut to the required precision. Most other companies cut them longer and trim to length, we were cutting directly to length. We weren't asking for more precision than normal, we were asking for the same precision in one cut instead of two. It worked--we were killing the competition but that didn't do any good when the housing collapse took out most of our business.

Consistency is accuracy. "Measure twice, cut once" is always good advice, but it takes twice as long.

 

[Loren Pechtel]

The objective was that the chop saws would cut to the required precision. Most other companies cut them longer and trim to length, we were cutting directly to length. We weren't asking for more precision than normal, we were asking for the same precision in one cut instead of two. It worked--we were killing the competition but that didn't do any good when the housing collapse took out most of our business.

Consistency is accuracy. "Measure twice, cut once" is always good advice, but it takes twice as long.

The cost of the higher precision was less than the cost of cutting twice. The company went under when more than 80% of our demand went poof.