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| why is the US not Metric |
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| vk6zgo:
--- Quote from: GlennSprigg on January 08, 2020, 12:44:18 pm ---Back on Page-42, (sorry), TimFox said... --- Quote from: TimFox on January 06, 2020, 04:04:45 pm ---As I understand the history, the liter was originally defined as 1000 cubic centimeters. The gram was originally defined as the mass of one cubic centimeter of water. The prototype kilogram was then fabricated to agree with that definition. However, due to the temperature dependence of water’s density . . . etc . . . --- End quote --- Actually, although these units of mass/size/volume were limited to Water, it goes so far as to technically specify that it was for Pure Water, at average Sea-Level, and at 21-deg C. :) On Page-43, vwestlife said... --- Quote from: vwestlife on January 07, 2020, 08:22:26 pm ---Anybody else remember these? Rulers marked in tenths of an inch, as a stepping stone to Metrication by decimalizing inches. They also tried to make the Metric equivalent easier to remember by rounding it off to "1 inch = 25 mm". (Hey, the Bible says Pi is 3.0, so isn't that close enough?) --- End quote --- Sorry, but in THAT regard, there was NO rounding off! It always was, & is, 1" = exactly 2.54cm. And yea, here in Australia, you can still buy, (in fact the most common), tape-measures with both metric & imperial. Comes in handy when you know/suspect something old was fabricated in imperial, so you don't measure something as say 381mm, when it was really 15" etc. Although I would rather add say 300mm to 450mm, then add 1' 4+15/16" to 1' 11+5/32" (unrelated comparison!) :D I don't think I ever saw 1/10ths of an inch on a ruler, (and I'm old), but of course measuring in 'Thou' on an imperial Micrometer was common, & fairly logical. Especially when relating that on Lathe dials! (Side-Note: Aren't Vernier Calipers a clever invention!! Although now electronically digital) P.S. I used to piss off an old Carpenter at work, ordering a piece of wood from him, say... 3' 7+5/32" and 274mm. He hated it, made it right! (He knew my humour though). :-+ --- End quote --- I'm even older, & back in the day, 1/10" divisions on the wooden school rulers was very common. (Linear graph paper had the large divisions at 1", & the small ones at 1/10".) The rulers also had 1/16' & 1/32" divisions on the other edge, but they were pretty roughly printed, so the 1/10" divisions were about the limit as far as readability was concerned. Not that it mattered much, kids don't commonly have to measure things to great degrees of precision in the classroom. Woodworking & metalworking classes had rules with better accuracy. |
| KL27x:
--- Quote ---Although I would rather add say 300mm to 450mm, then add 1' 4+15/16" to 1' 11+5/32" (unrelated comparison!) --- End quote --- I would also rather add 1' and 1.5' than 388mm and 282.9mm. (unrelated comparison!) >:D Not denying that fractions aren't more work. But this is why you avoid choosing stupid numbers in the design phase. And if and when you do, you work in just inches, not feet and inches. The place where one might end up with stupider fractions is often in stackups of thicknesses, in my own experience. But even in these cases, the dimensions are often nominal or not really perfect fractions of inches (and for things like plexiglass or plywood these are usually in metric, even, so you end up with imperial + metric). If you work with hardwoods, you often need to joint/plane all what you need for X project until they're all flat... then the thickness is wherever that ends up. This is where the calipers are handy, and thous save the day and unite all measuring systems, down to the precision that actually matters - no more, no less. The most common thing you would have to precisely "measure" or "calculate" is probably (in my world) for cutting slots, and in this case you might do it with a pencil or a marking knife (no measuring at all) or calipers. Definitely not a tape measure. From my perspective as a home/hobby shop in wood and metal working, there's a surprisingly little need to measure anything with fractions of an inch on the tape measure. Most often, it's just to make sure I have enough of w/e engineering material, to start with, and where to break it down. After that, it's more about symmetry and fit than exact numbers. The calipers/thous, squares, stop blocks, compass, marking gauges, pencils, and whatnot, are used way than 16ths of inches from a tape. No matter how close the marks, the tape is useless when it comes down to the fitting/joining, drilling holes symmetrically, et al. |
| CatalinaWOW:
Yep. You rarely use fractions less than 1/8 in rough carpentry, and even cabinet work rarely involves the smaller fractions. Usually only doing the last fit into a wall or something like that. The design took care of making small and uneven fractions un-necessary. I'm assuming metric carpenters use a millimeter as the smallest practical dimension for both rough carpentry and for cabinetry. A centimeter is just too big for either job. A millimeter might be a smidge big for some cabinetry work, but would suit in almost all cases. One result of working metric is that there might not be any strongly preferred dimensions. Perhaps even numbers. All of this is down in the noise of work efficiency and all that. A competent workman will handle either system well, with minor advantages in one situation or another for one of the systems. A true craftsman who didn't have to be mobile or have space limitations might even have tools for both systems and use whichever worked best for the task at hand. Which is more or less what I do, but my tools outrace my level of craftsmanship. Within hands reach as I type I have rulers graduated in fractions of an inch, (and also rules graduated in a variety of divisions from 20ths of and inch and 6ths of an inch to the one I use most, tenths), metric rulers, metric calipers, US std calipers and tape measures for both. Unfortunately I have to go a few steps to get a metric micrometer, the US STD one is in arms reach. This ability to hop back and forth, and my tendency to work on older equipment is why I am in no hurry to switch to 100% metric. Somebody who never intended to work on older stuff might do quite well with only metric gear. |
| KL27x:
--- Quote ---One result of working metric is that there might not be any strongly preferred dimensions. Perhaps even numbers. --- End quote --- Well, in metric home-contruction, they do have strongly preferred quantum steps. The 300 mm distance, which GlennSprigg mentioned, is a common "unit," which is a nice size (kinda like a foot) and also easily divisible by lots of factors. So when you frame a house, you can figure out the stud spacing and have two guys working on either end and be on the same page/grid. You just know different numbers to do it. Like is it 7,800 mm which is a multiple of 600? Or would it be 7,600, 8,000? The metric construction guy might know this from experience without thinking about it. The imperial worker might know the multiples of 4' or 16", better, by heart. (4' is 3x 16" stud spacing). The architect will know the standards to best make use of materials. It's not a big deal from the design/engineering, I think. I would guess it's more the cost to change the entire manufacturing and supply chain. We will get some different "standards," e.g. some countries use 700mL for liquor bottles, and some use 750mL. But probably not too much different from imperial. I get the feeling that metric manufacturers love increments of 25 grams/mm or 50 or whatnot, as they make smaller changes. Rather than using things like 720 or 730. So metric loves halves and quarters and eighths, too. ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; Some people think it's hilariously American that a housewife once described a Florida sink hole in the street as "big enough to swallow 10 washing machines." But compared to estimating dimensions which may require use of pi*R squared, I think these "washing machines" are actually a pretty good way to estimate/visualize the size of an irregular hole in the ground while under the gun. It's not like most people do this kind of estimation very often. If you want to figure out the mass of water it can hold, you can reverse-engineer this estimation. I'm going to guess around 15 cubic meters, give or take a top-loader vs side. I'm thinking just drop them in the hole, not change the shape of the hole to stack these things side-to-side. But if she said 15,000 liters or 500 cubic feet, would that be better for this question? I like the 10 washing machines, personally. If I ever see a sinkhole around this size, this washing machines will be my first unit of choice. :D |
| Zero999:
--- Quote from: KL27x on January 07, 2020, 10:56:37 pm --- --- Quote ---scale it by a factor of 5 --- End quote --- Can't you scale dimensions in any unit, though? Can you elaborate? --- End quote --- Of course you can. It's just more difficult, than sticking with one unit. You could scale linear measurements in inches just as easily as cm, or metres and the same could be said about a recipe in oz vs grammes. The problem occurs with imperial is more than one unit is normally necessary. Any tape measure longer than 60", has both feet and inches and weighing scales, for masses over a few pounds, have both pounds and oz. In reality you'll have 6"8', rather than 80", unless you're working on something quite small, which makes life harder, than just using cm. --- Quote --- --- Quote ---Angles are all fractions of a circle... The more unambiguously something can be defined, the better. --- End quote --- So... having and using both grads and degrees makes it more or less clear/ambiguous? Really, as long as you keep your usage focused for the task, you can use either in whatever the situation requires. French military might use degrees for navigation, but grads for artillery, for instance. But your whole post isn't making a lot of sense to me. --- End quote --- My point was just use one measurement, so keep it to degrees, as it's what everyone uses and the benefits of multiples of 10 don't apply to angles. Degrees, arcminiutes and arcseconds are pretty close to an optimum system. Angles often have to be measured very accurately, so saying 53o 43' 15" is much easier to read than a huge decimal number of decimal places. The only time it's inconvenient is it's often necessary to convert arcminiutes and arcseconds into decimals, but just sticking to one system or the other avoids that. --- Quote ---We use imperial for the highest levels of precision manufacturing/machining --- End quote --- As did the UK and most of Europe until we realised metric was easier to use, so we migrated towards it. No one is saying, imperial can't be used for precision engineering or scientific measurements, just that it makes calculations more difficult so isn't worth the bother. It's far easier to just use the SI system which is designed from the ground up. There's no point in having 50 or so different units for length, mass, volume, area, etc. just use one. Fair enough, in some cases, it might seem awkward to have 200g, rather than 7oz, or 0.3m, or 300mm, than a foot and it makes no difference in many applications, but it doesn't change the fact that life is much easier with one unified system. |
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