Eddy Current
Senior Member
I know that it is in 10's but what about the marks in between?
How do you read a metric ruler?
- Thread starter Eddy Current
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mivey
Senior Member
For a short ruler, the long marks are cm and the short marks are mm. You can say "2.35 cm" or "2 cm, 3.5mm" or whatever works for you.
For long tapes, you will usually see the dm mark indicated every 10 cm, and the meter mark indicated every 100 cm. You might say "4.2375 meters" "4 meters, 23.75 cm", or "423.75 cm", or "423 cm, 7.5 mm", or "4 meters, 23 cm, 7.5 mm" or whatever is prudent.
For long tapes, you will usually see the dm mark indicated every 10 cm, and the meter mark indicated every 100 cm. You might say "4.2375 meters" "4 meters, 23.75 cm", or "423.75 cm", or "423 cm, 7.5 mm", or "4 meters, 23 cm, 7.5 mm" or whatever is prudent.
Eddy Current
Senior Member
So what is the equivalent to say 1 inch and a half is it 1:5?
How?
I usually take my glasses of to read to the nearest millimetre....and, if I want better resolution, I use my digital vernier gauge.
Slightly more seriously, I'm from UK and we adopted SI units (what you probably think of as metric) in the electrical field a good many years ago.
I've just taken a look the 5 metre steel tape I keep in the kitchen drawer at home. It has dual measurements - Imperial feet and inches and metric.
The metric side is marked in centimetres as major units and millimetres (mm) as the minor units. Ten mm = one cm. Maybe that answers your question.
But, in my field, we rarely use anything other than metres and millimetres.
A typical conductor might be 2.5mm2 which gives the actual cross sectional area of the conductor as real number. It's a bit bigger that 14AWG but smaller than 12AWG.
But we buy it in reels of typically 100 metres.
An electrical control panel might be 800mm wide 2000mm tall and 500mm deep. A bit over 2.5ft by 6.5ft by 1.5ft.
We don't, as a rule use cm. Our packers do though so we have to give them dimensions in cm.
I have not seen the decimetre used for anything.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
120818-1542 EDT
The exact precise length of 1 inch is 25.4 mm. The (international) inch has been exactly 25.4 mm since July 1959.
In the late 1920s Carl Edvard Johansson, the inventor of the gage block, suggested that the exact definition be established as 25.4 mm. See
http://en.wikipedia.org/wiki/Carl_Edvard_Johansson ,
http://nvlpubs.nist.gov/nistpubs/jres/112/1/V112.N01.A01.pdf .
The National Bureau of Standards reference does not provide the reference to Johansson's suggestion that the inch be defined exactly as 25.4 mm, but it indicates indirectly that was his desire. At the present I don't know where to find the reference to Johansson's letter on this subject.
1926 to 1928 my dad rented a room from Charlie Anderson the brother in law of Johansson. Thus, they were family friends the rest of their lives.
Charlie Anderson was one of the toolmakers that did final lapping of gage blocks at Ford. The final operations in making gage blocks were performed in a temperature controlled room in the basement of the Ford Engineering Labs. In the mid 1940s Charlie Anderson showed me how he did the final lapping. An optical flat, and a mechanical gage that could measure with a resolution of about 1/1,000,000 inch was part of the measurement process. I wish I could remember the theory of that gage, but that was a long time ago.
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The exact precise length of 1 inch is 25.4 mm. The (international) inch has been exactly 25.4 mm since July 1959.
In the late 1920s Carl Edvard Johansson, the inventor of the gage block, suggested that the exact definition be established as 25.4 mm. See
http://en.wikipedia.org/wiki/Carl_Edvard_Johansson ,
http://nvlpubs.nist.gov/nistpubs/jres/112/1/V112.N01.A01.pdf .
The National Bureau of Standards reference does not provide the reference to Johansson's suggestion that the inch be defined exactly as 25.4 mm, but it indicates indirectly that was his desire. At the present I don't know where to find the reference to Johansson's letter on this subject.
1926 to 1928 my dad rented a room from Charlie Anderson the brother in law of Johansson. Thus, they were family friends the rest of their lives.
Charlie Anderson was one of the toolmakers that did final lapping of gage blocks at Ford. The final operations in making gage blocks were performed in a temperature controlled room in the basement of the Ford Engineering Labs. In the mid 1940s Charlie Anderson showed me how he did the final lapping. An optical flat, and a mechanical gage that could measure with a resolution of about 1/1,000,000 inch was part of the measurement process. I wish I could remember the theory of that gage, but that was a long time ago.
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John120/240
Senior Member
- Location
- Olathe, Kansas
Maybe so, but when all you have ever used is the inch, foot, mile Imperial system it is hard to change now.
Ounces you have to know whether you are measuring liquids or solids. This is one example
of our contradictory system
If there are ten spaces in between the numbers the little spaces would be 0.1 of the numbers... probably centimeters. So, if the measurement was 3 numbers and 4 little spaces the measurement would be 3.4 centimeters
The inch measuring system is really unhandy, and I think whoever came up with dividing things into eighths, quarters, and sixteenths musta had rocks in his head. Then, on top of that, there are twelve inches in a foot ... three feet in a yard... 5280 some feet in a mile (I think), don't even ask how many yards in a mile or inches in a mile...good grief, these people must been smokin' somethin'. Had something to do with some king's ego I think.
A meter is approx 39 inches long... If you are not going to convert from meters to inches you don't need to care how many inches long it is. Anything that is a meter long is a meter long and you don't care about inches. You have been using inches all your life, and you never cared how many meters your measurements were.
You already know how the decimal counting system works.... thousandths, hundredths, tenths, ones, tens, hundreds, thousands, ten thousands. Most everything in the metric system (SI) is based on a meter.... more particularly a tenth of a meter or a hundredth of a meter (centimeter) , or a thousandth of a meter(millimeter (milliamp?)) or a thousand meters(kilometer (kilobytes?)).
All you gotta do to change one to another is divide by 10 or multiply by ten... move the decimal point. 1 meter = 1000 millimeters = 100 centimeters = 0.001 kilometer (a kilometer is a thousand meters).
How you express a measurement depends on what units you use to express it... and you can use any you think is appropriate.
You likely wouldn't express a very long distance in inches or a short distance in miles.
If you are measuring something and it is 1 and 1/2 centimeters, you would say it was 1.5 centimeters. You could also say it was 15 millimeters. Something just a little shorter might be 1.3 centimeters. Something a little longer might be 1.7 centimeters. Something that was exactly in between 1.7 and 1.8 centimeters would be ....................... 1.75 centimeters ... you knew that.
What makes the whole thing difficult is changing from inches to metric and vice versa. If you measure a distance and tell me it's 350.6 centimeters, and I measure, mark, and cut a piece of conduit 350.6 centimeters, it's a piece of cake... we don't care how many inches it is.
But that's impossible.... and you know why.
The inch measuring system is really unhandy, and I think whoever came up with dividing things into eighths, quarters, and sixteenths musta had rocks in his head. Then, on top of that, there are twelve inches in a foot ... three feet in a yard... 5280 some feet in a mile (I think), don't even ask how many yards in a mile or inches in a mile...good grief, these people must been smokin' somethin'. Had something to do with some king's ego I think.
A meter is approx 39 inches long... If you are not going to convert from meters to inches you don't need to care how many inches long it is. Anything that is a meter long is a meter long and you don't care about inches. You have been using inches all your life, and you never cared how many meters your measurements were.
You already know how the decimal counting system works.... thousandths, hundredths, tenths, ones, tens, hundreds, thousands, ten thousands. Most everything in the metric system (SI) is based on a meter.... more particularly a tenth of a meter or a hundredth of a meter (centimeter) , or a thousandth of a meter(millimeter (milliamp?)) or a thousand meters(kilometer (kilobytes?)).
All you gotta do to change one to another is divide by 10 or multiply by ten... move the decimal point. 1 meter = 1000 millimeters = 100 centimeters = 0.001 kilometer (a kilometer is a thousand meters).
How you express a measurement depends on what units you use to express it... and you can use any you think is appropriate.
You likely wouldn't express a very long distance in inches or a short distance in miles.
If you are measuring something and it is 1 and 1/2 centimeters, you would say it was 1.5 centimeters. You could also say it was 15 millimeters. Something just a little shorter might be 1.3 centimeters. Something a little longer might be 1.7 centimeters. Something that was exactly in between 1.7 and 1.8 centimeters would be ....................... 1.75 centimeters ... you knew that.
What makes the whole thing difficult is changing from inches to metric and vice versa. If you measure a distance and tell me it's 350.6 centimeters, and I measure, mark, and cut a piece of conduit 350.6 centimeters, it's a piece of cake... we don't care how many inches it is.
But that's impossible.... and you know why.
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- Occupation
- Licensed Electrician
No it isn't. With metric there is no way to divide evenly into thirds.
I like thirds and so did the ancient Greeks. I have a few maxims in life, and one of them is you will be money ahead if you side with the Greeks.
Yes, that's one that throws Mrs B (she's from GA) through a loop when she's trying to cook something. The concept that fluid ounces in a US recipe is a volume and simply can't be taken as ounces as a weight, which is the only way we use them here when they are used at all, seems difficult for her.
Yes, assuming you want to do that, but metric (SI) has many more advantages that outweigh that minor inconvenience - if it is such.
For a start, there is just one unit for length, the metre. Other units are just decimal multiples or sub-multiples.
Similarly for volume, the litre.
And then there are the convenient relationships between the units. For example, a litre of water weighs on kg.
Inches aren't particularly thirds friendly either.
You can divide metric measurement using any calculator.
I just wish they'd go to one or the other... a lot of stuff that I come in contact with is a conglomeration of both.
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K8MHZ
Senior Member
- Occupation
- Electrician
Let's compromise. Like car tire makers did. Wheel diameter in inches and width in millimeters.
kwired
Electron manager
- Location
- NE Nebraska
realolman already said it, but is true, most of our units of measurement are not friendly with thirds. Time on the other hand which is consistant in all measurement systems, is more friendly with thirds. 1/3 minute, 1/3 hour, 1/3 day all are easily converted to another unit without any rounding off being necessary.
kwired
Electron manager
- Location
- NE Nebraska
realolman you also brought up kilobytes, but they don't quite follow the decimal system.
IIRC one kilobyte is actually 1024 bytes, one megabyte is actually 1024 kilobytes, and so forth. I don't fully recall why, but something to do with the fact there are 8 bits in one byte or something like that, making it an octal based system, and not a decimal based system, yet they kind of combined octal and decimal.
IIRC one kilobyte is actually 1024 bytes, one megabyte is actually 1024 kilobytes, and so forth. I don't fully recall why, but something to do with the fact there are 8 bits in one byte or something like that, making it an octal based system, and not a decimal based system, yet they kind of combined octal and decimal.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
120819-1449 EDT
kwired:
Most computers are based on the binary number system.
210 = 1024 decimal
1024d = 400h = 100 00000000b
220 = 210 * 210 = 1024d * 1024d = 1,048,576d
Why the binary system? Because it is easy, simple, inexpensive, and reliable to make bistable (binary) devices.
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kwired:
Most computers are based on the binary number system.
210 = 1024 decimal
1024d = 400h = 100 00000000b
220 = 210 * 210 = 1024d * 1024d = 1,048,576d
Why the binary system? Because it is easy, simple, inexpensive, and reliable to make bistable (binary) devices.
.
Eddy Current
Senior Member
Doesn't metric have something to do with numbers be divisible by 10 i thought i read that somewhere.
We've had one of our grand daughters stay for few days. Pretty as a picture and manners to match.
Today, her parents came to claim her back.
We sat around in the back garden and chewed the fat for a bit.
It's been hot and we discussed that.
"It was 86 degrees yesterday" I said.
"How much is that?" my daughter asked.
Engage brain........do the calculation......
"It's 30C" I tell her.
And a little and somewhat related tale.
One of my colleagues had a very nice play house that he wanted to dispose of, his children now being young adults.
He offered it to me knowing we had the grandchildren.
I, in turn, offered it to my daughter for her daughter. I sent pics and rough dimensions.
The next day the older girl, aged four, called me on the phone.
"Granddad B, I would like to have the house please."
How could you possibly refuse...
So, on Thursday, when we went to collect our little gem, we took it up there in one of the company vans.
For a play house, it was fairly large. About six foot by four foot and maybe seven foot tall at the apex of the roof. Despite being metric, we all could picture that.
Mr S, the dad, has put it together while the wee girl stayed with us.
We got to discussing how substantial the structure was and S said he had to climb on the roof.
"And I'm 13 stone" he said. Yet another Imperial measure. It's 182 pounds.
Interesting that, for one parent, degF was not meaningful yet both recognised Imperial dimensions.
Today, her parents came to claim her back.
We sat around in the back garden and chewed the fat for a bit.
It's been hot and we discussed that.
"It was 86 degrees yesterday" I said.
"How much is that?" my daughter asked.
Engage brain........do the calculation......
"It's 30C" I tell her.
And a little and somewhat related tale.
One of my colleagues had a very nice play house that he wanted to dispose of, his children now being young adults.
He offered it to me knowing we had the grandchildren.
I, in turn, offered it to my daughter for her daughter. I sent pics and rough dimensions.
The next day the older girl, aged four, called me on the phone.
"Granddad B, I would like to have the house please."
How could you possibly refuse...
So, on Thursday, when we went to collect our little gem, we took it up there in one of the company vans.
For a play house, it was fairly large. About six foot by four foot and maybe seven foot tall at the apex of the roof. Despite being metric, we all could picture that.
Mr S, the dad, has put it together while the wee girl stayed with us.
We got to discussing how substantial the structure was and S said he had to climb on the roof.
"And I'm 13 stone" he said. Yet another Imperial measure. It's 182 pounds.
Interesting that, for one parent, degF was not meaningful yet both recognised Imperial dimensions.
There are 10 millimeters in a centimeter. 100 centimeters in a meter. 1000 meters in a kilometer. 1000 millimeters in a meter
You and Gar are correct ... I just wanted to use something electrical in nature that used the kilo prefix meaning a thousand of something, in a similar way that milliamp means a thousandth of an amp. I didn't think of it being not quite exactly a thousand bytes... which it is not because it is a power of 2... but I think it does mean a thousand bytes
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