I'm old and set in my ways, but I am compelled and determined to learn and get used to using metric measurement. Is there some kind of simple metric tutorial on metric measurement? I don't need to learn the whole metric system...just the measurement part. I know it's so much simpler to do metric math. Right now I use a fractional calculator to do all of my imperial math.
Easy Metric Tutorial?
- Thread starter darita
- Start date
darita said:
What we call metric is technically the International System of Units, more info at Wikipedia http://en.m.wikipedia.org/wiki/International_System_of_Units
Here's a chart that helps (including the King Henry acronym (or is that an acrostic)): http://www.docstoc.com/docs/51839317/Metric-System-Chart-and-Table---The-Metric-System-is-based-upon
It's a fine system, it's the constant conversions here in the US that are a bear. This statement by me will probably shock some here since I'm often asking for the tools to have the option of inch marks. I've never said metric is bad, it's just not common here and is practically a foreign language.
darita said:
Well
mm = millimeter = 1/1000th of a meter
cm = centimeter = 1/100th of a meter
dm = decimeter = 1/10th of a meter
m = meter
Dm = decameter = 10 meters (dam also used as a symbol)
hm = hectometer = 100 meters
km = kilometer = 1000 meters
Edited to reflect comments made later by PaulG (thanks).
For a native metric user its really hard to know how to explain metric to someone who's accustomed to imperial measuments, but I'll try anyway.
As a measurement system the metric system is simplicity itself with everything a multiple of 10 i.e. 1 metre = 100cm = 10*10cm = 10*10*10mm (1cm = 10mm).
Metric math is simply just addition, subtraction, division and multiplication with normal base-10 numbers just like you would calculate money.
For example if we simplify a bit and say 1 inch = 25mm (I think its 25,4mm to be exact) then having a 4 inch board would equal to about 100mm which in turn equals 10 cm. If you want to rip that board in three equal width strips you just simply divide 100mm with 3 i.e. 100/3=33,33333mm (ignoring kerf width) you now aim at cutting at 33mm intervals to arrive at three 33mm wide strips.
Normally in metric you don't use exact fractions like in the imperial system you do i.e. you don't use notation of 33 1/3 instead you would write 33,33 in decimal and in woodworking you rarely need anything smaller than 1mm anyway, max 0,5mm resolution is achievable with even the sharpest knives much less with saws with a kerf of 2,2mm like the TS-saw blades.
In drawings it is customary to use millimetres i.e. table top lenght would be marked as 1200mm to denote a 1,2m long table top. Non-professionals often use centimetres instead and would write in the plan 120cm instead.
I find it easier to work in centimetres when you are on the better side of a metre i.e. 250cm instead of 2500mm or even metres when talking about long distances like 8.4m instead of 84000mm. Because everything is a multiple of 10 going from one unit to the next is just a matter of dropping or adding a zero to the end (or dividing/multiplying by 10).
Since the basic unit for all intents and purposes is 1 millimetre you don't need to worry about 1/32's or 7/16's etc.
You might want to learn some "standard conversion points" between metric and imperial. I use 25mm as an approximation for 1inch and multiples of an inch like 2x4 would be 50mm x 100mm, in plywood approximately 1/4" = 6,5mm, ½" = 12mm, 3/4" = 18mm (as standard thicknesses here are 4mm, 6,5mm, 12mm, 15mm, 18mm, 21mm, 24mm, 27mm and 30mm).
Probably getting a combination ruler/tape measure in the beginning may make the transition easier with visual aid to give you an idea how much is 37mm (1" 15/32).
I'm just as lost with imperial fractions and need a calculator or a conversion table to make heads or tails out of those pesky fractions.
Once you figure the metric measurement system out you will notice that the same logic works for volume as well i.e. 1 litre = 10 decilitres, 1 dl = 10 centilitres, 1 centilitre = 10 millilitres etc. (though usually no-one uses centilitres - only litres, decilitres and millilitres)
Welcome to the world of simple maths [big grin]
As a measurement system the metric system is simplicity itself with everything a multiple of 10 i.e. 1 metre = 100cm = 10*10cm = 10*10*10mm (1cm = 10mm).
Metric math is simply just addition, subtraction, division and multiplication with normal base-10 numbers just like you would calculate money.
For example if we simplify a bit and say 1 inch = 25mm (I think its 25,4mm to be exact) then having a 4 inch board would equal to about 100mm which in turn equals 10 cm. If you want to rip that board in three equal width strips you just simply divide 100mm with 3 i.e. 100/3=33,33333mm (ignoring kerf width) you now aim at cutting at 33mm intervals to arrive at three 33mm wide strips.
Normally in metric you don't use exact fractions like in the imperial system you do i.e. you don't use notation of 33 1/3 instead you would write 33,33 in decimal and in woodworking you rarely need anything smaller than 1mm anyway, max 0,5mm resolution is achievable with even the sharpest knives much less with saws with a kerf of 2,2mm like the TS-saw blades.
In drawings it is customary to use millimetres i.e. table top lenght would be marked as 1200mm to denote a 1,2m long table top. Non-professionals often use centimetres instead and would write in the plan 120cm instead.
I find it easier to work in centimetres when you are on the better side of a metre i.e. 250cm instead of 2500mm or even metres when talking about long distances like 8.4m instead of 84000mm. Because everything is a multiple of 10 going from one unit to the next is just a matter of dropping or adding a zero to the end (or dividing/multiplying by 10).
Since the basic unit for all intents and purposes is 1 millimetre you don't need to worry about 1/32's or 7/16's etc.
You might want to learn some "standard conversion points" between metric and imperial. I use 25mm as an approximation for 1inch and multiples of an inch like 2x4 would be 50mm x 100mm, in plywood approximately 1/4" = 6,5mm, ½" = 12mm, 3/4" = 18mm (as standard thicknesses here are 4mm, 6,5mm, 12mm, 15mm, 18mm, 21mm, 24mm, 27mm and 30mm).
Probably getting a combination ruler/tape measure in the beginning may make the transition easier with visual aid to give you an idea how much is 37mm (1" 15/32).
I'm just as lost with imperial fractions and need a calculator or a conversion table to make heads or tails out of those pesky fractions.
Once you figure the metric measurement system out you will notice that the same logic works for volume as well i.e. 1 litre = 10 decilitres, 1 dl = 10 centilitres, 1 centilitre = 10 millilitres etc. (though usually no-one uses centilitres - only litres, decilitres and millilitres)
Welcome to the world of simple maths [big grin]
mhch said:
I think you have that wrong.
Isn't a decameter = dam?
And a decimeter is your elusive 1/10 and is dm?
A hundred meters is a hectometer...hm
mm = millimeter = 1/1000th of a meter
cm = centimeter = 1/100th of a meter
dm = decimeter = 1/10 of a meter
m = meter
dam = decameter = 10 meters
hm = hectometer = 100 meters
km = kilometer = 1000 meters
Paul G said:
don't know but practically in wood work you would normally just use mm, cm or m.. and I for one just do everything in mm as feels the right balance between left and right of the decimal place.. I normally only go to 0.5mm accuracy (1/50th of an inch) so working in mm makes it easy
A standard kitchen worktop for example comes in 3m length, which is 300cm or 3000mm. Probably depends what trade you are in, I could imagine a roofer would work in m, due to accuracy required and long lengths of timber, as beams often come in lenghts like 2.4m, 3.3, 4.8, 5.2m etc
p.s. metric maths=decimals.... imperial=fractions, so metric should be easier, once you stick to a consistent unit of measurement
The difference between MM, CM and Meters is where you put the decimal point.
There are 10 MM in a CM
There are 100 CM in a Meter
If you took the measurement of 1111 MM
This could be expressed as 111.1 CM
or 1.111 Meters
They are all the same length, just a different or more convenient way of expressing the length. Its the same as 60 inches is 5 foot.
I always try and use MM and convert all my measurements to MM before I start. This just stops me making any errors when measuring, and I find MM the easiest to add, subtract and divide etc. as there is no decimal points to worry about unless you need a fraction of a MM.
To convert to MM is very easy, if your measurement is in CM's then times it by 10 to get MM
If your measurement is in Meters then times it by 1000 to get MM.
111.1 CM X 10 = 1111 MM
1.111 meters X 100 = 1111 MM
Hope that helps.
There are 10 MM in a CM
There are 100 CM in a Meter
If you took the measurement of 1111 MM
This could be expressed as 111.1 CM
or 1.111 Meters
They are all the same length, just a different or more convenient way of expressing the length. Its the same as 60 inches is 5 foot.
I always try and use MM and convert all my measurements to MM before I start. This just stops me making any errors when measuring, and I find MM the easiest to add, subtract and divide etc. as there is no decimal points to worry about unless you need a fraction of a MM.
To convert to MM is very easy, if your measurement is in CM's then times it by 10 to get MM
If your measurement is in Meters then times it by 1000 to get MM.
111.1 CM X 10 = 1111 MM
1.111 meters X 100 = 1111 MM
Hope that helps.
mattfc said:
There is no rule I'm aware of that says Imperial measures must be in fractions, that's just what is common. In my work in printing we use inches but mostly speak inch decimals, ie 1.1". I have many rulers that have inches divided in decimals as well. (actually we also use points and picas, but that's a whole other matter)
In metal working (perhaps I should say machined parts), it is normal to designate in decimal inches, most often to three decimal places (that's one thousandth of an inch); e.g., 8.382". Sometimes two decimal places are sufficient, and occasionally four decimal places are needed. Fabricated stuff (such as weldments, I-beams, etc.) is probably mostly in fractions on an inch, or maybe in feet ...
Paul G said:
You're right, I forgot things I learnt at school !! On the other hand, I wasn't totally wrong since Dm (upper case D) is used for decameter in addition to dam.
Sorry to add some more confusion to this topic.
In practice, woodworkers will only use mm and cm (rarely m I guess). Never saw any use of decimeter in practice, except to designate the 2 dm long wooden stick marked with a scale, typically called a "double decimeter" (translated from French), that was used at school many years ago for drawings. No one uses it anymore.
Decameter, hectometer, and kilometer are mostly used to express road distances and property dimensions.
mhch said:
Which reminds me of this one:
A Texas rancher decides to return to old Blighty to rediscover his English heritage. He visits his great uncle, a yard farmer, and asks him how far his land extends. "All the way down there to the street," replies the yard farmer, gesturing proudly. The Texan chuckles. "I could drive all day long and not reach the end of my property." His uncle replies, "I used to have a car like that."
sorry for going OT, couldn't resist
Best, Karel
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As an engineer, I bounce back and forth between the two systems quite often. Many times even mixing the two within a single design. (However, drawings are always in one set or the other unless dual dimensions are given for when metric is required, such as screw threads. You never mix units unless there is some specific reason, and that includes the metric system too.)
The imperial system is not as bad as popular misconception portrays it. The main benefit of the metric system comes into play only when you need to convert units. If you don't need to convert units, that primary benefit is not terribly important. For example, converting cubic centimeters to liters is very simple, but that is not a conversion that the average person needs to do very often. Converting millimeters to meters is also very easy, but generally speaking, you still don't want to mix units, even when those units are just multiples of 10. Regardless which system you are using, you pick a unit and stick to it throughout.
The most common complaint about the imperial system is fractions. However, that is a "choice" not a "requirement". We "choose" to buy tape measures that are graduated in fractional increments. However, they are also available in decimal divisions too. That's not a fault of the system of measurement. It's just a choice that has been long-standing. Most machinists and engineers work in decimals, not fractions. And in that regard, there is no difference between the systems unless you want to convert to a different unit.
We "choose" to portray measurements in mixed units, such as 10' 3-1/4", as opposed to 123.25", but that is a choice, not a requirement. The same mixing of units could be done in the metric system, but it just isn't done. You will rarely see a mixed unit measurement of 1m 4cm 2mm. Instead, if the precision of millimeters is required, then the entire number is represented in millimeters (1042mm).
Neither system is any more accurate than the other. It is just different units.
Personally, I find it easier to "guesstimate" the length of a board in inches, than I could in centimeters. But that is simply due to familiarity, and the larger size of an inch versus a centimeter.
The imperial system is not as bad as popular misconception portrays it. The main benefit of the metric system comes into play only when you need to convert units. If you don't need to convert units, that primary benefit is not terribly important. For example, converting cubic centimeters to liters is very simple, but that is not a conversion that the average person needs to do very often. Converting millimeters to meters is also very easy, but generally speaking, you still don't want to mix units, even when those units are just multiples of 10. Regardless which system you are using, you pick a unit and stick to it throughout.
The most common complaint about the imperial system is fractions. However, that is a "choice" not a "requirement". We "choose" to buy tape measures that are graduated in fractional increments. However, they are also available in decimal divisions too. That's not a fault of the system of measurement. It's just a choice that has been long-standing. Most machinists and engineers work in decimals, not fractions. And in that regard, there is no difference between the systems unless you want to convert to a different unit.
We "choose" to portray measurements in mixed units, such as 10' 3-1/4", as opposed to 123.25", but that is a choice, not a requirement. The same mixing of units could be done in the metric system, but it just isn't done. You will rarely see a mixed unit measurement of 1m 4cm 2mm. Instead, if the precision of millimeters is required, then the entire number is represented in millimeters (1042mm).
Neither system is any more accurate than the other. It is just different units.
Personally, I find it easier to "guesstimate" the length of a board in inches, than I could in centimeters. But that is simply due to familiarity, and the larger size of an inch versus a centimeter.
