There's more to a ground-source heat pump than just effectively 'moving heat with a lower expenditure of energy'. The ground source can be treated as a near-infinite source and sink of heat energy at from 55 to 57 degrees F depending on latitude and soil conditions ... and this is good for two things: you can pretemper the air exchange, and you are no longer trying to 'force' the heat into already very hot air in summer or very cold air in winter, a major cause of inefficiency in "conventional' HVAC heat-pump setups (and a reason why most honest ones are dual-fuel).
If I remember correctly, the circ pump on the ground loops in a Water Furnace is a fractional-horsepower synchronous AC motor. and this small amount of power alone accounts for an enormous saving of effective compressor energy any time the outside climate goes out of temperate conditions.
Erik -
You're quite right - I do know that heat pumps don't create heat (or cold), but merely move it from one place to another. I overlooked that principle in my haste to finish the post early this morning. [As supplemental info, the coefficient is said to be ~4, so it (WaterFurnace) would be running 65 to 80 % of the time, which seems about right for our experience on the coldest winter night. (The rest of the winter electric bill difference might be explained by running the water heater a little more, cooking warmer foods, running the clothes dryer instead of outside line drying, etc.). At other times - such as bright sunny days - the passive solar heating alone supersedes it (typ. 71 deg. in that zone, with the thermostat set at 68 deg.), and/ or when the fireplace insert/ stove is burning. Someday I want to put usage meters on each 220v device in the house (heat pump, water heater, cooktop, oven, and clothes dryer, etc.) and measure how much each actually consumes during the winter vs. summer.]
Back to railroading: I wonder what the 'ton' rating was for the ice blocks for the early air conditioning in the Pullman cars and cooling function in the refirgerator cars; and then for the later mechanical systems in each ?
- PDN.
Paul_D_North_Jr I didn't know about the 1 lb. force @ 1 mph = 2 Watts, but it correlates pretty well (1/2% or so) with what I often use: 1 HP (550 ft.-lbs./ sec.) = 746 Watts. Both are also rail-related when working on electrification studies.
I didn't know about the 1 lb. force @ 1 mph = 2 Watts, but it correlates pretty well (1/2% or so) with what I often use: 1 HP (550 ft.-lbs./ sec.) = 746 Watts. Both are also rail-related when working on electrification studies.
Or discussing the efficiency of electric transmissions on diesel loconotives.
IIRC, 1 ton of heating/ cooling capacity** = 12,000 BTU, so my 3-ton ground-source ("geothermal") heat pump will be using about 10.5 kW at full power (~$1.27 per hour, $30 per day). Fortunately, that happens about never . . . ~$5 - $6 per day is a more typical average figure for the heating season, maybe $1 - $2 / day during the cooling season.
You're forgetting that a heat pump is called that for a reason, that is uses mechanical work to pump heat from a colder location to a warmer location (same thing a fridge or freezer). I suspect that a ground sourced heat pump would be good for a coefficient of 3, which means the heat output is three times the mechanical work in. Running full tilt, your heat pump would consume closer to $10/day and your bill suggests that the system is running ~50% of the time.
The traditional reason for expressing power plant heat rate in BTU/kwhr is that coal is spec'ed on the basis of BTU/lb, sold by the ton, while electricity is sold by the kwhr.
- Erik
erikem . . . HO scale at 3.5mm/foot and 1 lbf at 1 mph equalling 2W. I still remember 1 kwhr equalling 3412 BTU.
Btu is one that's hard to know intuitively (at least for me). "It is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. One kilowatt-hour (kWh) of electricity contains 3,412 Btu."*
**"A ton is the cooling capacity of an air conditioning system. One ton is equal to the amount of heat required (288,000 Btu) to melt one ton of ice in a 24-hour period. A one-ton air conditioner is rated at 12,000 Btu per hour (288,000/24). A two-ton unit would be rated at 24,000 Btu per hour."*
* https://www.nwnatural.com/uploadedFiles/ConnectToGas/StepsToGetGas/FAQ/FAQs_The_Definition_of_Cool.pdf
My classes in thermo and fluid mechanics were done in both SI and English Engineering units. English engineering was easier when pressures were pounds per square foot, density in slugs per cubic feet and velocity in feet per second. Pressure is a funny one as units still in use include psi, pascals, inches of mercury, millimeters of mercury (Torr), bar and atm. Velocity is another one as the most commonly used units are km/hr and mph.
A few of the at least somewhat common metric/English hybrids are heat rate for power plants in terms of BTU per kwhr, HO scale at 3.5mm/foot and 1 lbf at 1 mph equalling 2W. I still remember 1 kwhr equalling 3412 BTU.
As I recall, a few items - viscosity of fluids (centipoises ?), some flow rates of quasi-solid materials (thixotropic ?), and some biological reactions (as in sewage treatment plants) were in metric units.
Haven't touched some of those in years (decades ?), so I may well be incorrect, and will welcome any corrections.
Clearly, SI is easier mathematically but I have no feel for it. I admit I may be old fashioned (I'm 58) but I have a better feel for one pound per square inch than one newton per square meter, as an example.
I got to enjoy Thermo in both English and Metric sometimes both in the same problem ...
RME AnthonyV When I was in college, I stumbled upon a ASME paper advocating that the U.S. should switch to the metric system and touting the benefits of doing so. It was dated in the 1880s But the U.S. did switch to the metric system, a decade before that (even before joining the CGPM), and its standards have been nominally metric-based ever since. I suspect that as long as base measurements for engineering under SI are either in mm or km, there won't be much groundswell for practical engineers here to utilize it -- there's enough trouble trying to do things with non-graphics-based 'drafting' programs and such to consider adopting and then trying to use utterly inconvenient units that leave orders-of-magnitude ambiguity in the coefficients. With the advent of good calculators, any reason for a formal switch to SI on 'this side of the pond' isn't nearly as important as it previously might have been. It's only when people start forgetting rigorous attention to their calculations, or leaving out defining their units (both of which I thought were still part of any engineer's fundamental education) that trouble with spacecraft and such crops up. I never learned thermo in anything other than metric ... but it's cgs, and will remain resolutely so, whatever mise en pratique silliness Sevres might cook up next.
AnthonyV When I was in college, I stumbled upon a ASME paper advocating that the U.S. should switch to the metric system and touting the benefits of doing so. It was dated in the 1880s
But the U.S. did switch to the metric system, a decade before that (even before joining the CGPM), and its standards have been nominally metric-based ever since. I suspect that as long as base measurements for engineering under SI are either in mm or km, there won't be much groundswell for practical engineers here to utilize it -- there's enough trouble trying to do things with non-graphics-based 'drafting' programs and such to consider adopting and then trying to use utterly inconvenient units that leave orders-of-magnitude ambiguity in the coefficients.
With the advent of good calculators, any reason for a formal switch to SI on 'this side of the pond' isn't nearly as important as it previously might have been. It's only when people start forgetting rigorous attention to their calculations, or leaving out defining their units (both of which I thought were still part of any engineer's fundamental education) that trouble with spacecraft and such crops up.
I never learned thermo in anything other than metric ... but it's cgs, and will remain resolutely so, whatever mise en pratique silliness Sevres might cook up next.
In all my engineering classes in the late 1970s and 1980s, the English system was the dominant system of units. Thermo, fluids, heat transfer, and mechanics was taught using the english system with some SI. Machine design and strength of materials was taught exclusively using the English system with a homework problem or two in SI
AnthonyVWhen I was in college, I stumbled upon a ASME paper advocating that the U.S. should switch to the metric system and touting the benefits of doing so. It was dated in the 1880s
When I was in college, I stumbled upon a ASME paper advocating that the U.S. should switch to the metric system and touting the benefits of doing so.
It was dated in the 1880s
Getting back to slab-track junctions, and the original question that all the 'blather' came out of:
PDN was wondering about various motions and deflections at the joints in slab-track systems, and used a Cartesian axis 'convention' that didn't account for some of the potential motions. Since we have one of the world experts in specification of degrees of freedom of mechanical systems not only present in these forums but reading this thread, let me ask this:
What would be the BEST convention to use in specifying axes and degrees of freedom for railroad track analysis? PDN saw this looking down on the track in plan, I think x being nominally longitudinal and Z being normal to the plane of the track as measured, say, across the railheads. That simple convention, as he noted, didn't account for rotation of the slab ends if the slabs were to bow or otherwise deflect on expansion, which could be considered as being relative to other defined axes. What should the framework or conventions be for best fit of model with intended purposes?
The immediate question is whether the Canadians who still use mpg are tying it to Imperial gallons. I'm still old enough to remember Esso receipts from fishing trips (to the Cabonga reservoir, which then still had plenty of pike longer than I was tall no matter what units of length you used) and was struck by just how much bigger the imperial gallon seemed.
Strange that Canadians don't use 'liter numbers' for drink sizes; perhaps because Americans tend to love their soft drinks (and perhaps also because there might be some validity to that wretch Bloomberg's assertion that supersize sodas can cause deleterious mental effects) the recognition of 'two-liter bottles' as a vernacular term is just about pervasive. You'll still have 16-ounce size (in part due to conflation of fluid and avoirdupois measures in the American tradition) but it helped that 500ml is a "bonus" size, and what American doesn't love the sense of getting a little for free (especially Cajuns who have a special word for the thing).
Nixon and Congress missed a sure bet, and the Carter administration, really dropped the ball on getting distance metricization adopted for roads here. If we had to have an arbitrary reduction of speed limit (for fuel consumption, although of course spun to the marks as "safety") it should have been set relative to effective truck gearing, somewhere around 62.5mph and not asinine 'double nickels' supposedly easier to remember. Now, everyone loves and respects 'the ton' in the way folks used to use the expression 'going like sixty', and here was a convergence of events on that nice, round 100km/h (or kph as we said at the time). Instead we got a memorable 88, then went to the enforcement strategy of encouraging cops with a speed-trap mentality to assist our national priority, and no, America didn't decide to come along. I no longer often see km/h equivalents on Interstate signage, which indicates for the nonce that the 'popular transition' to a system adopted here almost 150 years ago now is once again stalled.
I don't look at the Mars lander thing nearly as forgivingly as you and many others do. Engineers know to pick consistent units, define their terms properly, and periodically check. What they were doing with English measure for orbital calculations is still something I can't figure ... and a great many people evidently made the same assumption, that decimal calculations would be in 'scientific' metric units. Now there are some stupid metric conventions, too, like there being no nomenclatural safeguards at all between notation in mks and cgs (perhaps typically, the answer coming out of Switzerland was to deprecate the system most actual scientists were using) and when I first heard about the incident I thought that ws the cause. For it to be English calculations assumed to be metric was bad comedy indeed ... but that wasn't the worst part. Folks from JPL being involved in such a thing was the inconceivably bad part.
erikemI may be mistaken, but isn't the USGS inch slightly different than the US standard inch? (USGS 39.37in/m, standard 1in=0.0254m).
I think it may be a rounding convention, not definitional in the sense of all those variant inches and toises and pouces, oh my!
The fun thing about defining an inch to be 25.0mm would be that a foot would come out to 0.3m and then be about 0.1% longer than a light-nanosecond as opposed to 1.6% longer.
Just my little bit to help Grace enlighten the kids.
Thing was that in 1876 it still might be possible to transition industrial production from 'old inches' to 'new inches', perhaps with some tolerance adjustments to make the effect "the same" where factor of safety or other fit due to the .04 was not critical. That is not as radical a shift as, say, the adjustment in the "official" American speed of sound when it turned out everyone was pulling their measurements toward an 'accepted value' that turned out to be consensual but aberrant. like some other activity concerning significant figures.
The 12" foot (and 18 or 20" 'cubit') may still cause some pain, but then again we still don't have decimal time (in America, at least, we did the decimalization logically; it's where you get the six-second increments on a cell-phone bill, or the six-minute time increments set up for my wife's cleaning business...) If you don't like feet, stick with machinist's decimal inches for a combination of haptic magnitude and high precision in one measurement ... and use some sort of despised 'new yard' to stand in for meters on longer measurements. (Note that the 2.5 conversion leaves the 'yard defect' worse instead of better, now only 0.9m, so we'd still be two cultures separated by a common metric as far as distance measurements were concerned, and the cumulative 'error' between new and old distance measures does begin to tell at surveying magnitudes...
Might as well bring up a prank I pulled on my 7th grade geography teacher. One of the questions on a test was the height of a mountain (think it was Mt Cook in Kiwi land). The teacher was foolish enough not to specify which units for the answer, so I gave the answer in inches. Fortunately the teacher had a good sense of humor.
One of the zeroth laws of science I was taught very early in life was 'always specify your units'. Had that convention been followed we would probably know somewhat more about Mars. It is as true for dane teachers as for those in nerdy fields... and, come to think of it, what if you'd answered in furlong/firkin/fortnight units? That teacher reaction might have been fun to see.
On the other hand, I remember a cautionary tale from a teaching seminar somewhere: in an elementary math class, the teacher wanted to know how many "numbers" there were between two integers, say 6 and 9. A student answer -- key to this is that demeanor, tone of voice,etc. were lamentably absent, as with much Christian Scripture -- was 'five', and upon being told that was wrong and to explain their answer, said "6.5,7,7.5,8,8.5" The teacher reportedly told him to sit down and shut up as a wiseass. The seminar presenter was aghast that such a lovely teaching moment had been wasted (shades of those teachers in "Despotism"!) I had the uncomfortable realization that the student might have understood more about mathematics, but was more interested in making the teacher look bad... balancing truth and discipline has often been something of a problem in the Western tradition...
Paul_D_North_JrWe were confident of that tolerance, and that note was accepted, so "end of problem" as we say. In comparision, with the steel standard you cite, for the length of 43 m the tolerance would still be only 6 mm ~1/4 inch, so both of our tolerances are essentially identical.
Paul, I have been lucky and found the standard in internet which is very rare.
There are too classes. The higher requrements are: L = LengthL < 30 m: 16 mm30 m > L > 250 m 0,2 x (L + 50) mm L in meterL > 250 m 0,1 x (L + 350) mm
At 43 m that would be approximately 19 mm. But stricter tolerance requirements are possible.Regards, Volker
RME- Well I for one rather enjoyed your humorous and enlightened foray into the SI system. Up here in the great white north I am a hybrid existing within another hybrid. Pierre Elliot Trudeau saddled us with the metric system beginning in 1970, I think mainly to give the USA the middle finger. I was well into my 20's and grew up and educated in the Imperial System. So that's the first one. The second is that while Canada has long since converted there is still significant use of non metric units and standards in many sectors of the Canadian economy and every day use. This is due to historical ties with the United Kingdom, proximity to the United States and public opposition....nobody uses kg's for anything except packaging labelling on products, which nobody gives a hoot about,... ask any Canadian how many mL a can of coke is and you will get a blank stare despite the fact its printed right there in front of them every day. Nobody expresses their height in mm. Not doctors, not anyone. We still calculate mpg for our cars, although that one is fading. L per 100 km...what? Too many variables in play for that one. Home builders, carpenters and construction use feet and inches, period.
As for temperature we are 100% Celsius and the best I can come up with is that it really sucks, especially in the home. So both systems are in widespread general everyday use by everyone. Only exception is the "elites" who walk around thinking they are so much smarter than the rest of the Neanderthals, as in all my wooden headed addle brained fellow profs. In the Mills, mineral processing, both systems are in widespread use.
I do worry that the USA will eventually cave so please see to it that you don't. Let me guess, California, Oregon and Washington State, then no one else. That's ok.
BaltACD- I have never, and will never, ever, understand that. All those brains, all those people, all the checks, all the money ...like what? It's a bad comedy line from a terrible comedian that you can see coming.
erikem RME Many of my European friends try to trot out that tired old "whose inch do you use" without recognizing it is European inches and national prides that were the root of the problem in the first place. An international convention that standardized on a legitimate human-scale metric, like an "inch" at 2.5 "cm" could easily resolve all that petty stupidity at a stroke. I may be mistaken, but isn't the USGS inch slightly different than the US standard inch? (USGS 39.37in/m, standard 1in=0.0254m). The fun thing about defining an inch to be 25.0mm would be that a foot would come out to 0.3m and then be about 0.1% longer than a light-nanosecondas opposed to 1.6% longer. OTOH, with 30 years being about a billion seconds, estimating a light year in feet is easy - about 33 quadrillion feet. Might as well bring up a prank I pulled on my 7th grade geography teacher. One of the questions on a test was the height of a mountain (think it was Mt Cook in Kiwi land). The teacher was foolish enough not to specify which units for the answer, so I gave the answer in inches. Fortunately the teacher had a good sense of humor.
RME Many of my European friends try to trot out that tired old "whose inch do you use" without recognizing it is European inches and national prides that were the root of the problem in the first place. An international convention that standardized on a legitimate human-scale metric, like an "inch" at 2.5 "cm" could easily resolve all that petty stupidity at a stroke.
Many of my European friends try to trot out that tired old "whose inch do you use" without recognizing it is European inches and national prides that were the root of the problem in the first place. An international convention that standardized on a legitimate human-scale metric, like an "inch" at 2.5 "cm" could easily resolve all that petty stupidity at a stroke.
I may be mistaken, but isn't the USGS inch slightly different than the US standard inch? (USGS 39.37in/m, standard 1in=0.0254m).
The fun thing about defining an inch to be 25.0mm would be that a foot would come out to 0.3m and then be about 0.1% longer than a light-nanosecondas opposed to 1.6% longer. OTOH, with 30 years being about a billion seconds, estimating a light year in feet is easy - about 33 quadrillion feet.
Of course we have had Mars landing space craft with the trajectory's calculated in the wrong measurement system and make a 'hard landing' from which the craft did not survive.
Never too old to have a happy childhood!
I had been spending at least a few seconds of blather time wondering what possible relationship machine-tool standards could possibly have to ballastless fixed-track structure. Or geodesy, for that matter.
That still hasn't been explained, coherently or otherwise. But I no longer have any interest in reviving it, or discussions of humorous exaggeration in units of measurement, or ... well, any of the diversions away from ballastless approaches to track construction.
We had Mr. Landwehr, who I suspect works directly on some of these things, about to engage MC, who has seen some American failures of the concept, over best practices in design and build. We also had some interesting discussions going about how this type of structure would handle CWR forces, what would be needed for accidents like flooding or ground settlement below the subgrade prep, and how the need for frequent control joints across one system of slab track came to be so necessary as to be called out as a feature of construction. We need to take those subjects up again.
I have not been back to reply which I see has given you plenty of time to engage in meaningless blather about units of measurement which have absolutely nothing to do with coordinate syetems. Any appropriate units can be used. No one has yet told what this "Z" and "Y" are.
International standards for machine tools? Here ya go:
ANSI/ASME B89.3.4 NAS 938 ISO 841 DIN 66217 and EIA 267-C .
ChuckCobleigh mudchicken Thankfully there's significant figures that can come to the rescue. Or not. I was reminded by our sparkling, warm weather of late of my days as an undergraduate at San Diego State (College, then) when the Spring semester soon heralded the unveiling of many significant figures on campus, which coincided with many GPAs of male students plummeting. Might have done better going to a cold weather school. (Not!)
mudchicken Thankfully there's significant figures that can come to the rescue.
Thankfully there's significant figures that can come to the rescue.
Hallo Paul,
+/-1 mm tolerances are for manufacturing in a workshop. I never heard of problems. I should have mentioned that the given values were element measures. For steel structures there are different erection tolerances. Regards, Volker
Volker -
Thanks for that explanation and examples. Those are generally entirely reasonable and practical tolerances, with the possible exception of the shorter ones for steel. Allowing only 1 mm or 1/32" for a 78-3/4" length of steel seems too small to me; I would ask to use 1/8" ~3 mm instead except in unusual circumstances.
A few years back, we had to measure / stake-out a distance on the order of 140 ft. (~43 m) - for the construction of the glass facade of a building - to a shown dimension with a precision of 1/16 inch, ~1-1/2 mm (you can see it at N 40.63378 W 75.45410 ). Some discussion with the installation subcontractor revealed that it really didn't need such accuracy, because of temperature variations and a sliding (roller) bearing, etc. What they really wanted much more certainty as to the accuracy than was usually the case - but we still had to certify to the distance. So I did, subject to the following note, as I recall it: "+/- 1/4" (~0.02 ft. or 6 mm). We were confident of that tolerance, and that note was accepted, so "end of problem" as we say. In comparision, with the steel standard you cite, for the length of 43 m the tolerance would still be only 6 mm ~1/4 inch, so both of our tolerances are essentially identical.
If those close tolerances can be consistently achieved - and European standards are world-class quality, as many of us know - then that's great.
Hello Paul,
we have a DIN Standard that governs the tolerances independently of the measuring units. The tolerances dependend upon the length of the measured element. For length up to 3 m the allowed tolerance is ±12 mm, 3 to 6 m: ±16mm; for 6 to 15 m: ±20 mm; 15 to 30: ±24 mm; >30 m: ±30 mm.
Steel structure tolerances are much smaller: 1 mm for length up to 2,000mm and 6 mm at 16,000 mm in steps of one mm in-between.
If there are 5 elements in a row the total length is the basis. If you have 5 elements of 6 m length each has a tolerance of ±16 mm, the tolerance of the row is ±30 mm.Steel structure tolerances are much smaller. Steel structure tolerances are much smaller. ±1 mm for length up to 2000mm and ±6 mm at 16,000 mm in steps of one mm.
Smaller tolances can be contractually agreed.
Thas has been just one example. All possible deviations are regulated.Regards, Volker
[Groans in mock pain from that pun]; then
Also belongs over on the Not So Improved Humor thread, and some kind of engineering humor collection.
People should understand the difference between 0's as "placeholders" and real values. E.g., 20, 20., 20.0, and 20.00 can have 4 different meanings, respectively: +/- 1/2 interval of 5 ft. for the first, and likewise +/- 0.5 ft., 0.05 ft., and 0.005 ft. for the others, respectively.
Which is one reason why I write the 'cents' portion of my checks the same as in a 'legal description' of a deed for real estate - e.g., "Twenty dollars and no one-hundredths cents" or "Forty Six and Twenty-Three one-hundredths Dollars for $46.23. (You can imagine some of the side effects to that idiosyncracy - but never has anyone refused to accept or cash a check written in that manner. MC, stop laughing when you can . . . )
Volker, I too am a civil engineer, and so would like to ask what magnitude of tolerances you apply to those dimensions ? 1 mm ~1+/ 32nd of an inch, which is generally way too fine for any outdoor application of the sort that's the subject of this thread (except for the cross-section dimensions of the steel rails and steel fasteners, etc.). Measurements truly like that will have to be specified and compensated for temperature (either scale, as long as it's consistent), or have a tolerance of - say, +/-3 mm at minimum - to have any hope of being faithfully replicated in the field.
Here in the US, the cross-slopes of sidewalks and the Americans with Disabilities Act (ADA) handicapped ramps (i.e., the the yellow or red rectangular plastic panels with the truncated cone bumps) usually cannot exceed 2% without a waiver. That's usually interpreted as 2.0% using a digital Smart Level, which means that across their typical 5 ft. width, the elevation difference cannot exceed 0.10 ft. ~ 1-1/4 inches, with a maximum + tolerance of 0.005 inch ~ 1/16 of an inch before the slope is 2.1%, which is non-conforming. Considering that the ramps and sidewalks do need do some slope for rain water to drain off them properly - say, 1% - the allowable elevation difference is reduced to 0.05 ft. As I like to say, those are tolerances for interior finish carpentry, not civil field construction, which is the point of this paragraph.
In contrast, measurements of concrete to the nearest meter (length or volume) is way too coarse unless a truly massive structure such as a dam is being built. There's an informal principle among construction field inspectors to usually - unless specified otherwise - measure for payment to 0 decimal places (for this, the nearest inch, which ~0.08 ft. ~0.1 ft. practically), calculate to 1 decimal place (for this, 0.1 cubic yard), and pay to 2 decimal places (here, 0.01 of a dollar or 1 cent).
As I've said before elsewhere, 0.01 ft. or 1/8 is a convenient and practical measurement for surveying and construction field work. Metric units are not practical: 1 mm ~1 plus/32 of an inch, which is generally much too fine and implies false precision; and 1 cm ~3/8", which is too coarse when better precision and accuracy can be achieved easily.
And calculated or measurements of characteristics such as the Tractive Effort of steam locomotives that are purported to be closer than to about the nearest 1,000 lbs. are false precision (see LeMassena's Numbers essay that I referenced above.)
And further I sayest not.
tree68I'm surprised the cubit hasn't come up (or did I miss it?)
You didn't see it. I doubt you missed it. [note: where is the smiley for 'rimshot'?]
One of the most 'useful' canonical definitions of a cubit is 18", or 1.5 feet. That is remarkably close to 500cm, or 0.5meter. So if, say, approximating distance with a forearm, someone in the field might choose this for estimating in whole units in either system. It's about the longest effective dimension of human scale that can be used to measure distance (the fathom, or distance on Leo's Infinite Man between outstretched fingertips) being longer but difficult to apply consistently or without a helper/spotter...)
It has a conceptual defect in that it isn't an even multiple of 2.5 (the 'standard inch' representation in nominal cm) which can be fixed by standardizing a cubit around that ... say 20" for a more precise half-meter.
Or the "stone."[/quote]
Don't ask me to defend it. Any more than I'd defend English pre-decimal currency, even where there are reasons for it (wasn't the silver groat the unit that was supposed to make cab-fare more convenient in the 1830s?) as tradition is a miserable substitute for engineering convenience. I note we have recently touched on that most ridiculous of the English units, the 'hundredweight', in conjunction with where 'doing the ton' came from; it takes a puissant empire, indeed, to make a unit like that commonly-used.
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