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Metric vs Imperial - Practical or Traditional?

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Peter G. Shaw04/11/2010 19:18:51
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Chris,
 
mm ARE preferred units, as are meters & kilometers. What is NOT preferred is cm, ie centimetres, but unfortuately certain misguided people insist on using it on the totally spurious grounds that it is more useful, or easier to understand, or something.
 
Which I cannot understand as people use grammes & kilogrammes without having to use centigrammes. In the electronics world people have long been used to working in factors of 1000 (including 0.001), so why on earth do people have to use a totally useless and  irrelevant centimetre. And increasing to possibility of an error to boot, ie by allowing the usage of different factor of 10.
 
I mean, if we are going to use additional factors of 10, then why not also use the decimetre, and really create confusion?
 
Regards,
 
Peter G. Shaw
chris stephens04/11/2010 19:36:14
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Hi Peter, 
Is not the SI system based on the older KMS which was of course based on the cgs system (which probably why people got used to using the centimetre unit )
K  is of course Kilogram
M is for Metre (not you will note mm, cm, or any other minor or major unit)
S is for Second 
chriStephens 
Stub Mandrel04/11/2010 21:05:39
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When I was at school we invented a unit called the 'Arb'; we felt that the regular use of arbitary units was loose and unprofessional and wanted a good solid system we could rely on. You could measure anything with it with impunity, so unlike the limited imperial and metric measures you could use a single unit to measure length, weight, time and anything else really. Think about the fuss around exactly fixing the Avogadro constant? Solved in a trice, just use a random number of Arbs, and make sure you stick to it for the rest of your calculation.
 
Neil
 
John Olsen04/11/2010 22:35:59
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While the metre, kilogram and second are the base units in terms of which other units are defined, that does not mean that you are not allowed to use other units at all. The preferred style is to use multipliers that are powers of three (or multiples of three), hence kilometer (10^3) or millimetre (10^-3) and so on. But I don't think that "preferred style" means that a policeman will grab your collar if you choose to use centimetres here and there.
 
The main drawback with metrics, and it applies to inches and thou too, is that pesky little decimal point, which can so easily disappear or get confused with a flyspot on the paper. Why can't we have a more visible delineator? (There is also the fact that the continentals use the comma and the dismal point the opposite way around to what the rest of us do...)
 
regards
John

Edited By John Olsen on 04/11/2010 22:37:23

Versaboss04/11/2010 23:02:59
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A lot could be said from a continental viewpoint to the above statements:

- it is not forbidden to use centimeters. A carpenter or a mason - afaik - does not work in mm.

- the correct dividers/multipliers are: milli = 1/1000; centi = 1/100; deci = 1/10; deca = 10; hecto = 100, kilo = 1000. A centigram would be 0.1 g or 100 mg. In Austria it is very common to use dekagrams (e.g. in recipes)

- The comma as decimal point is used in Germany for currency values, e.g. 3,90 Euro; but not in engineering (measuring) contexts. In my country we use always the point.

The REAL difficulty - as seen from here - is that it is not possible (here) to obtain material in imperial dimensins. So using 3 mm steel instead of 1/8" leads to much arithmetic(and errors)  in changing dependent dimensions. 

And, btw, I think this theme is now fully  beaten to death...

Greetings, Hansrudolf

chris stephens04/11/2010 23:10:04
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And thanks to Microsoft we can't even put our decimal point in the right place, we have to use a full stop instead.
chriStephens
PS I did not mean that we can't use suitable prefixes where necessary, it is just that the SI system , which is the system under which the ISO works, only recognizes the base unit Metre and no other. It is obvious that for convenience there are separate names for both larger and smaller divisions. It is much easier to say zero point zero zero zero zero zero oneM as Mu.
One problem we could overcome with the metric measurement scheme is the unfortunate fact that the smallest unit most of us work to in metric has no convenient name, unlike the IMP system which has a "thou". I therefore propose that we, as model engineers, give a name to the smallest unit on a standard metric micrometer ie one hundredth of a millimetre, that name should I feel be a DaMu (pronounced Damn-you) which is made up from the symbol Da meaning 10 and Mu a millionth of a metre. 10 micron being a 1/100th of a mm. Sorry for using fractions but they do have their use even in metric. The only other name could be a "HUN" short for hundredth of a mm, but then ones significant other might think you were calling for a coffee, if spoken out loud.

Edited By chris stephens on 04/11/2010 23:20:30

Eddie05/11/2010 07:57:25
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Hi
The bottom line is the egg was laid.
Accept that one work in Units that they are comfortable with.
I use both.
Woodworking is still in Inch standards; Think a little about the odd sizes metric wise that wood working equipment and timber is sold in.
Depending on the plans at hand I switch between standards or convert to metric.
I still say; Personal preference prevail.
Eddie
Howard Jones05/11/2010 09:30:02
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I laid out my last piece of earthwork in cubits.
'cause it was easiest.
truely.
KWIL05/11/2010 11:04:12
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Chris, 21·52 looks like a decimal point to me in Microsoft Word as pasted


chris stephens05/11/2010 12:58:54
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Hi Kwil
I was thinking about the MS standard keyboard, which only produces full stops, even when using the numbers pad on the right. 
chriStephens 
Howard Jones05/11/2010 14:26:16
70 forum posts
112 photos
in Kwil's post above, highlight the decimal point, then place the cursor over the highlight
and right click the mouse. select 'view selection source' from the menu.
Kwil you've used a symbol font.  Chris's point remains correct.
Ian Abbott05/11/2010 18:32:45
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Some years ago in Canada, pre CAD, I had to translate the metric dimensions and redraw the plans of a new theatre, so that the occupiers could use all their Imperial drawing templates and equipment.
When I came across measurements of 5715 mm, my mind switched off until I realised that it was a nice even 225 ft.  I discovered as I went on, that the designers had drawn an Imperial theatre, because all of the materials were in feet and inches.  After it was all finished, they sat down with a calculator and changed all the measurements to millimetres and drew it at 50:1 instead of 1/4", making the plans impossible to use with imperial lighting and scenery templates.  I swear that they had a copy in Imperial which they refused to give us.
 
And, on probably fifty percent of the odd jobs that I make parts for, I don't use any measurements.  Turn a piece of metal to something that looks right, then bore a hole until it fits.
 
Ian 
KWIL05/11/2010 18:51:43
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Of course I used the symbol font just as I would if I were typing an article that requires a decimal point, merely showing that you can provide the decimal point if you need to. As Chris said he was refering to a standard keybord entry, which was not stated in his original as he subsequently informed us.
Peter G. Shaw05/11/2010 20:36:05
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Chris,
 
The following from Tubal Cain's Model Engineer's Handbook, with suitable abreviations:
 
"Both the 'MKS' (note the order of letters) and the 'cgs' systems have been abandoned in favour of SI."
 
"The SI system is now universally adopted in science, and is almost so in engineering...."
 
"The 'preferred' prefixes are those which go up and down by 1000 at a time....  In length, therefore, the centimetre (1/100 metre) is not used in engineering practice and though it may be retained in domestic usage (eg in dress-making) it is best avoided even here."
 
Just for the record, most of the time I use metric - SI units. If using these units, I will NOT use anything other than mm, m or Km, and if people are incapable of understanding it, then that's their hard luck - they will have to learn, and learn quickly *. I do use imperial - if it happens to suit, eg when measuring a length, it may be that the imperial graduations line up whereas the metric ones don't.
 
* I do realise just how this sounds, but having been on the receiving end of a salesman who quite obviously did not understand what he was talking about, and read reports of the crap, to be blunt, that some salesmen talk in an attempt to sound knowledgable, I now no longer care what these people think. Generally speaking it's their loss when I walk out because they don't know what they are doing.
 
On the other hand, those salesmen who do use correct terminology are the ones who will make the sale, even if they don't understand it!
 
Regards,
 
Peter G. Shaw
 
 
 
Terryd05/11/2010 21:21:55
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Hi Ian,
 
5715 mm = 18' - 9" not 225' - 0"
 
QED
 
T

Edited By Terryd on 05/11/2010 21:27:53

Terryd05/11/2010 21:26:57
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Hi Ian
 
P.S.
 
225 feet = 68.58 metres. 
 
Something wrong here!  I'd like to see that theatre.
 
T
blowlamp05/11/2010 21:31:17
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5715 mm = 225 inches.
 
Martin.
Terryd05/11/2010 21:45:00
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225 inches = 118" - 9" as I said
 
5715mm does not equal 225 feet as Ian Stated!
 
It may be similar to Chris Stevens decimal point problem except someone mixed up feet and inches - could lead to interesting results.  But silly me mistakes aren't likely in the Imperial system - are they?
 
QED
 
T

Edited By Terryd on 05/11/2010 22:04:15

Stub Mandrel05/11/2010 21:54:47
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Don't blame Microsoft for that one, its the ASCII standard's fault!
 
Neil
Nicholas Farr05/11/2010 21:55:30
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Hi Terryd, I think you were right the first time.
 
Regards Nick.
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