Metric measures

[Bob D.]

Coincidentally Matthias Wandel showed a Metric/Imperial rule he created
just the other day in a YT video. Have a look.

 

[Sanderxpander]

It's obvious I'm not going to convince anyone and I don't even really have to, I'm fine using mm for dimensions and do so most of the time. But to say the conversion between mm and cm, which literally means shifting the decimal point one place right or left, "destroys" the advantage over the imperial system with twelve inch feet and lots of different fractions sounds really strange to me. Cm/mm is just a non-issue.

 

[Bob D.]

Agree, I'm in my 60s and back in grade school we were being taught the metric system because "it's right around the corner" and "the US will be on the Metric System by the time you graduate High School". Yeah, that never happened.

Anyway, I wish we (the USA) had 'converted' years ago. Maybe then I would not have 40 years worth of tooling in my home shop designed around the Imperial measurement system. Yes fractions seem daunting if you have not used them much but it's not too bad. It's not much different than learning a language I think.

Also, at work I'm stuck with drawings from the 60s, 70s, and 80s when the place was designed and built. Those will never be converted (too expensive, over 500,000 hand-drawn drawings, not CAD, so not easy to scan and convert to DXF or DWG) to metric so kinda stuck with Imperial there.

You can't work on your car or pickup with a set of metric tools for the last 20 years I'd say. Maybe in another century we'll catch up with the rest of the world. Hang in there, it will be here before you know it.

 

[AlexThePalex]

Centimeters defeat one of the primary benefits of metric over inch.  With mm, almost everything you do is whole units, not decimals. Needing less than 1mm is un-common, yet 1mm works out nice as a base thickness.  Even in engineering work it's nice as most all dimensions are whole mm numbers. Not many things get over 1m, and when they do mm still work fine up thru 10m. 1mm is ~.040" which is a classic big tolerance, and 0.1mm is a good tighter tolerance limit  .004" (aka about 1 sheet of paper).

Just re-read this, odd understanding of engineering you have, I must say.

I did the first year of engineering school, didn't finish my whole study because I got side tracked, but what we learned is that you have different tolerances for different applications.

And for working with metal, the standard tolerance is measured in thousands of a millimeter, 0,001 mm or micrometer. Engineers don't mind decimals, there is nothing wrong with decimals. They are very used to decimals.

Working with decimals is not the same as working with fractions. Want to add 0,123 + 0,456 ? That's simply 0,579.

But want to add 3/8 + 5/6? You'll have to convert to 1/24th! Very complicated to work with and you e.

"Not many things get over 1m, and when they do mm still work fine up thru 10m" - You know bridges and skyscrapers are also made by engineers, right? Trucks, tables, even a fridge is easily over 1 meter.  Engineers don't mind, they simply convert.

 

[waho6o9]

Use a 5M folding ruler and enjoy the day.

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[Sanderxpander]

It's in cm, that's too complicated, apparently.

On a more serious note, I would love to hear about high quality measuring devices that use millimeters exclusively. I'd probably try one out. My Starrett combo square, my incra ruler, my Bosch laser meter and my Stanley tapes and folding rulers all use centimeters.

 

[DeformedTree]

Centimeters defeat one of the primary benefits of metric over inch.  With mm, almost everything you do is whole units, not decimals. Needing less than 1mm is un-common, yet 1mm works out nice as a base thickness.  Even in engineering work it's nice as most all dimensions are whole mm numbers. Not many things get over 1m, and when they do mm still work fine up thru 10m. 1mm is ~.040" which is a classic big tolerance, and 0.1mm is a good tighter tolerance limit  .004" (aka about 1 sheet of paper).

Just re-read this, odd understanding of engineering you have, I must say.

I did the first year of engineering school, didn't finish my whole study because I got side tracked, but what we learned is that you have different tolerances for different applications.

And for working with metal, the standard tolerance is measured in thousands of a millimeter, 0,001 mm or micrometer. Engineers don't mind decimals, there is nothing wrong with decimals. They are very used to decimals.

Working with decimals is not the same as working with fractions. Want to add 0,123 + 0,456 ? That's simply 0,579.

But want to add 3/8 + 5/6? You'll have to convert to 1/24th! Very complicated to work with and you e.

"Not many things get over 1m, and when they do mm still work fine up thru 10m" - You know bridges and skyscrapers are also made by engineers, right? Trucks, tables, even a fridge is easily over 1 meter.  Engineers don't mind, they simply convert.

I'm not sure where you are going with this.  This isn't about fractions v decimal.  We don't use fractions, but sadly when working with inch stuff, even though you work with decimals, the values used are generally decimal fractions  (.125, .375, .750) The point I'm making along with others is that metric gives you a great system to work with, and jamming cm in there along with mm at the same time is just asking for mistakes, see my example above.  I know from previous discussions you use cm, that doesn't change the matter that globally when working in metric cm are not generally used.  The cm-kg-s system is obsoleted for m-kg-s and or mm-kg-s.

On tolerances, I'm not sure where you were taking issues.  Some of this may be a difference in how metric prints and inch based prints are generally toleranced.  Inch prints typically have a sheet tolerance block.  Tolerance in inch based world is based on places after the decimal.  So in the lower corner of a drawing there will be a block that looks something like this  :  .X  +-.1 , .XX +-.05  .XXX +-.025 .  (the actual values are up to the company to decided, and is generally based on what they build).  In the field of a drawing,  if  there is a dimension that is 12.5"  then it has a tolerance of +-.1  if it says 12.50" then it has a tolerance of +-.05".    if  .125  then +- .025".  The number of decimal places dictates the tolerance.  If you want to be different from the default, then you call it out in the field.  12.500 +- .004, this trumps the block.    You can do the same with metric, and update the values of things.  Of course in metric trailing zeros don't matter.    12.500 is the same as 12.5  also there are now leading zeros  0.5, not .5".  Metric drawings generally use range tolerances.  Something like  0-10mm +- something.  10-100mm +- something.  I'm not sure if that plays into your comment on tolerances. Handling of leading and trailing zeros in metric vs inch systems is completely different. With inch based stuff you almost always have decimals places in play because an inch is a big unit of size.  If you were to work in cm, you will still have the same annoyance as working in inches. But by working in mm, especially for doing something like house construction, you are never going to go into decimal places. Everything will be whole numbers, life is great.

With modern machining we can expect to hold sub .004"  (.1mm) all day.  So this is where working in mm is very nice.  Just call out dimensions in mm, and have sheet tolerance for no place to be something like +-1mm (.039", nice loose easy tolerance), and when you need tighter, you have .X tolerance as +-.1mm.  So it's a very convenient setup.  Of course GD&T changes it all, stuff is now basic, but that works great with mm too, again all whole numbers and you only see decimals in the Gtol block.

It comes down to things being the right scale, and that's why mm are so nice.  Far as when you shift to m from mm,  no idea what various industries do.  I know we stick to mm all around, and stuff we build gets rather large.  I've worked on stuff near 10m long, everything was still mm.  As needed a jump to meter from mm is easy enough. Certainly no need to jump to meter on a house, only extremes of the house get very big.

But there is no reason to use cm, we don't talk in cm, we don't design in cm, standards/specs for things aren't in cm.  So it comes down to why inject something in there for no reason.  Stuff is generally listed/talked about in  mm and m.  Long distances we will make the jump to km, and for things like surface finish um,  why toss cm in there?  If someone is making cabinets, it's 32mm cabinetry, the material is in mm thickness, the hardware/slides are in mm, Festool marks their tools in mm (parallel guides as a good example, and the tracks are designated in mm too), everything being done is in mm, so why would someone want to use a cm tape measure and risk the mistakes like I showed above?

switch to mass for a moment,  we work in grams and kilograms.  Sure kg may be a bit big of a unit for  some things, and gram may be a bit to small for things, but we stick to gram and kg,  we don't don't randomly decide to use centigrams.  If you bought a scale and it read out in centigrams, sure it works and yes you can convert easy enough. But will a person make mistakes, you bet and often.

 

[Sanderxpander]

When I take a measurement of, say 62.6 cm on my tape measure, I write down 626. There's no chance I could ever think I might have meant 626 cm, same as you don't mistake 6 inches for 6 feet. When I have to use a tape measure again to transfer the measurement, I add in one decimal point and it's 62.6 again.

The simple fact is that millimeter based measuring devices are not common and often not practical for the kinds of distances we need (in the sense that the numbers won't fit in a sensible way). But you can easily read a cm based tape measure as a millimeter based one that just has numbers every tenth millimeter and a larger mark every fifth.

 

[DashZero]

METRIC is easy just like the money here in USA.

10 penny = 1 dime
10 dime = 1 dollar
100 dollar bill = 1 100 dollar bill

I never could see where the confusion is here.

 

[DeformedTree]

When I take a measurement of, say 62.6 cm on my tape measure, I write down 626. There's no chance I could ever think I might have meant 626 cm, same as you don't mistake 6 inches for 6 feet. When I have to use a tape measure again to transfer the measurement, I add in one decimal point and it's 62.6 again.

The simple fact is that millimeter based measuring devices are not common and often not practical for the kinds of distances we need (in the sense that the numbers won't fit in a sensible way). But you can easily read a cm based tape measure as a millimeter based one that just has numbers every tenth millimeter and a larger mark every fifth.

Life would just be easier to have a truly mm tape measure, then you wouldn't be going back and forth.  But look at my example I gave above.  It's not that one is going to think one or the other. It's about when you go to mark things and get screwed up in the way I described above, it's very easy to do. It's just an oddity that tape measures show in cm (generally), yet nothing else does.  Machines with readouts are inches/mm , same for calipers and a lot of other measurement tools.  Drawings are in mm, etc.  Why does one thing in the whole system report in cm.  I'm sure a lot of it is people who make the tapes just go with it because all the other tapes before did it.  I like rule 2 printed right on the tape of the fastcap tape "remove the opportunity for mistake from the process".

 

[demographic]

When I take a measurement of, say 62.6 cm on my tape measure, I write down 626. There's no chance I could ever think I might have meant 626 cm, same as you don't mistake 6 inches for 6 feet. When I have to use a tape measure again to transfer the measurement, I add in one decimal point and it's 62.6 again.

The simple fact is that millimeter based measuring devices are not common and often not practical for the kinds of distances we need (in the sense that the numbers won't fit in a sensible way). But you can easily read a cm based tape measure as a millimeter based one that just has numbers every tenth millimeter and a larger mark every fifth.

There may be a misunderstanding about how I do this but thats basically what I do.
I have a tape that reads in cms and I automatically convert to mms straight away, I never ever write down a size in cms.
Any apprentice I have gets trained to do the same so they can give me a size to cut something to or vice versa without having to explain it too much 170 always means 170mm, none of this 170 cms stuff.
They are on my tapes but as far as. e using them is concerned they only exisf in theory, never as a spoken or written size.

Furthermore, on the sites I see using cms marks someone out as being a possible chancer, that's in the UK though, when I was working in France a few years ago and went into a builders merchants asking for a 600 concrete lintel they looked at me like I was crazy because they work in cms so it would be six metres long.

 

[AlexThePalex]

The cm-kg-s system is obsoleted for m-kg-s and or mm-kg-s.

Cm is not an SI unit, and the scientific community must use SI units. But do you think a carpenter is a scientist?

On tolerances, I'm not sure where you were taking issues. 

You said in engineering everything is measured in whole millimeters. I gave the example of tolerances to show engineers works with decimals constantly. It's the norm. Because of tolerances.

It comes down to things being the right scale, and that's why mm are so nice.

Exactly, and cm is precisely the scale that relates most to humans. If your girlfriend ask you the size of your pee pee, do you say 150 mm? No. 15 cm.  [wink]

But there is no reason to use cm, we don't talk in cm, we don't design in cm, standards/specs for things aren't in cm.  So it comes down to why inject something in there for no reason.  Stuff is generally listed/talked about in  mm and m. 

We don't talk in cm? We talk in centimeters ALL the time. Constantly, every day. We just can't shut up about them. But of course we're inhabitants of metric country. What do we know.  [tongue]

switch to mass for a moment,  we work in grams and kilograms.  Sure kg may be a bit big of a unit for  some things, and gram may be a bit to small for things, but we stick to gram and kg,  we don't don't randomly decide to use centigrams.  If you bought a scale and it read out in centigrams, sure it works and yes you can convert easy enough. But will a person make mistakes, you bet and often.

It is just a matter of habit. You can't relate how people talk about mass to how they talk about size. Size and distance is a much more occuring measure for people than weight is.  So for weight we're happy using the two most common units, grams and kilos. For size, and distance we use four. Millimeters, centimeters, meters and kilometers. Your gf will not ask you how much your pee pee weighs, just how long it is.

PS, if there's anything in my post our beloved moderators can't live with, just PM me and I'll erase your concern.  [embarassed]

 

[Cheese]

I try to stick to one unit of measurement to reduce possible confusion and more importantly error. So for me it’s millimeters or inches. 

And even for 2x materials and boards, I still use inches up to about 12 foot. It’s just easier to remember 139 3/8” than 11’ 7 3/8”. Especially if you’re trying to remember 2 different measurements at the same time.

So for me cm is just another distraction. My Starrett scales and Woodpeckers scales are all in inches or mm. That’s the way God wanted it...[poke]

 

[Jiggy Joiner]

In the UK, some old die hard trades work in feet and inches, and they end up making mistakes, and costing themselves money when wrongly converting. They are too stubborn to learn the metric system but, hey, each to their own.

The majority of trades over here work in metric, and most of those in millimetres. A lot of the public (non trade) people use CM's as they were probably taught it at school, and feel after a measurement goes past 9mm they have to use CM's, and after 100 CM's they start stating metres etc, etc.

Most aspects of construction use millimetres, joinery companies, replacement window and door companies all work in millimetres.
Most bricklayers, and plumbers do too, and many suppliers.

Although as I mentioned last time this came up.
Some shops sell in LBs & oz as well, as or instead of grams and kilograms. Then of an evening, we might call a taxi, to take us to the pub, on the way to the pub, the taxi gets low on fuel, the driver is in a rush but, observes the 30mph speed limit, and pulls into the petrol station, and puts 25 ltrs of petrol into the cab. Then proceeds to the pub, when we arrive, we pay in pounds Sterling (decimal) money.
We get to the bar, and I order a well deserved pint of beer for me, and a white wine for Mrs Joiner. Outside is a shellfish stool, he's selling prawns, how much I ask? do you want a pint, or a kilo? says the stall holder.

Simple really  [big grin] [tongue]

 

[DeformedTree]

The cm-kg-s system is obsoleted for m-kg-s and or mm-kg-s.

Cm is not an SI unit, and the scientific community must use SI units. But do you think a carpenter is a scientist?

Why would it matter,  the idea is one system to rule all. 

On tolerances, I'm not sure where you were taking issues. 

You said in engineering everything is measured in whole millimeters. I gave the example of tolerances to show engineers works with decimals constantly. It's the norm. Because of tolerances.

I think you mis-read or something.  Engineering is certainly not in whole mm.  The point I was making that when designing in metric/mm things work out very nicely that almost nothing is ever going to go below a whole mm outside of tolerances and such.  I wasn't saying the resolution of the engineering world is 1mm units.  If you have a part,  your going to not likely to have a dimension like 95.5mm on it, you will probably be 95 or 96.  In the inch world we don't get such a niceness as you really can't design much if you never go sub 1". 

It is just a matter of habit. You can't relate how people talk about mass to how they talk about size. Size and distance is a much more occuring measure for people than weight is.  So for weight we're happy using the two most common units, grams and kilos. For size, and distance we use four. Millimeters, centimeters, meters and kilometers. Your gf will not ask you how much your pee pee weighs, just how long it is.

PS, if there's anything in my post our beloved moderators can't live with, just PM me and I'll erase your concern.  [embarassed]

Yeah, it is habit.  Being pro-cm is a bit like those who are pro-inch.  Definitely you live in an area that speaks in cm,  even without talking to you I am use to the regionalism with cm.  I know there are pockets in Europe were they are commonly used.  I've had co-workers from Europe, some spoke in cm, some did not. But they generally learn to move on from cm because else where as has been mentioned by myself and others it's either inches or mm. Also living in country that is stuck with inches I know all too well the issues that come up with cm.  If you try to convince people of the value of the metric system, a centimeter is seen as just a different sized inch, it's different but doesn't help them any any way, it's just different.  Those who bash usage of the metric system use the silliness of a cm as part of their case.  But also it's what confuses people.  When I have got people to remove cm from their mind and just use mm and m, the system comes around to them a lot easier.  Nothing they will measure in general usage will matter sub mm, now it starts to make sense, no more decimal place for the most part.  And from a human perspective mm is great.  a mm is about as small as a person is going to notice by looking.  If your laying stuff out, between your pencil mark, and some fudge in tools, marking, etc. You will probably get the mark plus/minus 1mm.  This works out just fine, if your building stuff, you generally stop at around 1/8th or 1/16th of an inch. So that error in your marking is well within "good enough".  If you do need to go finer, .1mm is great for folks to comprehend because of the similarity to paper.  People have a sense on the thickness of paper, you can't really see it, but you can feel it. Much below that, folks can't really feel very much.  So it's a good bottom threshold for people to keep their head around.  Other folks I have known have commented along the same lines that once they gave up on cm, and started thinking mm, they came around to the whole thing.

For sure if you grew up in a world like you did with cm as the conventional unit, it will seam fine and you won't see the issue with it. Again it's not different than those who see inches and fractions as being fine and being natural and making sense.  Or to leverage another topic we have had, it's like wanting to stick to 110V (the centimeter of electricity) power.  Why go all 240V, when 110V and 240V work perfectly well together  [wink] .

You get North America to go 230V, and the rest of the world can worth on freeing the Netherlands from the centimeter  [big grin]

 

[Bob D.]

I think you're all making a mountain out of a mm.   

 

[AlexThePalex]

But they generally learn to move on from cm because else where as has been mentioned by myself and others it's either inches or mm. Also living in country that is stuck with inches I know all too well the issues that come up with cm.  If you try to convince people of the value of the metric system, a centimeter is seen as just a different sized inch, it's different but doesn't help them any any way, it's just different. 

Nobody is moving on from cm. There are no issues with cm. Where do you get these ideas? Certainly not in places that actually use metric. Conversion between mm, cm and m is done all day without effort or confusion.

The scientific community made the SI system to avoid confusion because their high end applications required more clarity in cross-communication. But the scientific community is just a very small percentage of the world, and for the vast majority that are the rest it doesn't matter.

Those who bash usage of the metric system use the silliness of a cm as part of their case.

Who bashes the metric system? That 5% of the world population still living in the imperial age? Yeah, good case.

Funny how those who don't use the metric system find 500 reasons what wrong with it, but those who actually use it don't think twice about it.

 

[Sanderxpander]

When I take a measurement of, say 62.6 cm on my tape measure, I write down 626. There's no chance I could ever think I might have meant 626 cm, same as you don't mistake 6 inches for 6 feet. When I have to use a tape measure again to transfer the measurement, I add in one decimal point and it's 62.6 again.

The simple fact is that millimeter based measuring devices are not common and often not practical for the kinds of distances we need (in the sense that the numbers won't fit in a sensible way). But you can easily read a cm based tape measure as a millimeter based one that just has numbers every tenth millimeter and a larger mark every fifth.

There may be a misunderstanding about how I do this but thats basically what I do.
I have a tape that reads in cms and I automatically convert to mms straight away, I never ever write down a size in cms.
Any apprentice I have gets trained to do the same so they can give me a size to cut something to or vice versa without having to explain it too much 170 always means 170mm, none of this 170 cms stuff.
They are on my tapes but as far as. e using them is concerned they only exisf in theory, never as a spoken or written size.

Furthermore, on the sites I see using cms marks someone out as being a possible chancer, that's in the UK though, when I was working in France a few years ago and went into a builders merchants asking for a 600 concrete lintel they looked at me like I was crazy because they work in cms so it would be six metres long.

So actually you use cms all the time and convert to millimeters anf back without even thinking about it. And the order of magnitude between them is so great that even when your workmates were used to speaking in centimeters the situation was quickly resolved because they realized you couldn't possibly mean that.

I think we really do the same thing, I don't understand the "issue" with centimeters as you've just demonstrated there is none.

 

[Jiggy Joiner]

I much prefer to work in millimetres and have no reason to include centimetres.
I’ve also noticed that when discussing measurements with clients, suppliers and architects, all is just fine until somebody introduces cm’s or mtrs into the conversation.
Usually lots of mumbling and placing of decimal points follow.

I remember when decimalisation was first introduced, many weren’t interested and said why change? Then apart from because we are getting more involved in the EE, being given as a reason, we were also told for accuracy.
It was banded around that a millimetre was a very small and precise measurement, that could be split if required but, mainly because of how everything was derived from a single millimetre, up in multiples of 10’s, 100’s 1000’s etc, to very large measurements.

On Monday morning I have to go and quote a job, it’s a small extension with a couple of roof lanterns, and some large either sliding, or bi folding glazed doors to the rear and side.
I am meeting the client and a roofer there, I bet the only person who won’t be talking in millimetres, will be the client.

 

[DeformedTree]

I much prefer to work in millimetres and have no reason to include centimetres.
I’ve also noticed that when discussing measurements with clients, suppliers and architects, all is just fine until somebody introduces cm’s or mtrs into the conversation.
Usually lots of mumbling and placing of decimal points follow.

Yup, have had meetings where the one person uses cm and throws people off, especially if you are in a country that defaults to inches.  When you work on stuff that is always different and generally doesn't have a baseline to work from to have an idea how big the thing someone is talking about it, it gets very confusing.  If you work on the same stuff all the time, that is always more or less the same size, it's going to be less confusing.