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Is there a standard symbol set? 2

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vagulus

vagulus

Mechanical
Apr 22, 2014
51
In the study of Engineering I am constantly plagued by the haphazard use of symbols. The latest offence was this (from my textbook which shall remain unidentified to protect the guilty [wink])

Use_of_N_md4nxo.png


My author has moved from using 'N' for Newtons to using it for rpm (arguably, for a Number of rpm) without pausing for breath.

Everyone will have seen this lack of consistency; everyone will have their favourite horror story. However, before we censure anyone for lack of discipline we have to establish whether the rules for such discipline exist. Therefore, my question is, "Is there an accepted standard set of individually distinctive symbols for engineering values? Since I haven't been able to find one, I am of the opinion that such does not exist (I would appreciate being corrected [bow]) so I have to add the question, "Is such a thing possible?



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Well, of course not. Have you considered how many quantities and constants there are? A VERY typical error in Mathcad is to define something like m=5kg and then use it in something like PE=mgh, and wind up with kg*J/m

So, there, m for mass, m for meter.

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Be happy you're not in the concrete industry. Their code uses symbols not even found in the thousands available through Microsoft.
 
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Even within Mathcad, there are anomalies. The SI symbol for gram is g, so kilogram is kg, etc. In Mathcad, g was assigned to the standard value of gravitational acceleration 9.80665, so gram becomes gm, while kilogram remains kg.

Nevertheless, you can look at for standard accepted usage of units.
Or the CODATA Recommended values of physical constants: You can easily see conflicts, e for electron charge or for Euler's constant. F for the Faraday constant or for farad? R for the gas constant or for the Rankine?

Life used to be much simpler; there were fewer things that we knew, and most disciplines didn't interact with others. That's no longer the case.

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You're just confusing variables with units' symbols. There's no inconsistency (offence) here. Force, F (N). Rotational velocity N (rpm) or ω (rad/s).

Many people make problems for themselves by using unit names as variables. I often see "rpm" as a variable name (in computer programs and formulae). I've never seen "N" as a force variable though, and your author clearly doesn't use it either.

Steve
 
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Furthermore you can Google "ISO TR 25679 2005" and download free
 
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"My author has moved from using 'N' for Newtons to using it for rpm "

It looked to me italicized N was used for rpm, and non-italicized N for Newtons.

My recollection is lower case N (n) appears for rpm from time to time in some industries.
like this -

Yes, a reference table up front would seem to be good manners.

I find the use of acronyms by various industries has always been confusing, but nowadays has become far worse. Seems like if I'm not " in the club " I am not welcome.
 
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I too see no offence in using N for Newtons then N for angular velocity. In one case it is used as the universal SI symbol for the Newton, a unit of measure. In the other case it is use as a variable. These are two different purposes that pose no conflict in the same article.


Tunalover
 
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Thanks to all who contributed to that discussion. [thanks] May I summarize -

Somptinguy and tunalover both picked up a point I think lies an the base of the issue:
Many people make problems for themselves by using unit names as variables. I often see "rpm" as a variable name (in computer programs and formulae). I've never seen "N" as a force variable though, ...

Tmoose also makes the valid point: ... a reference table up front would seem to be good manners.

Perhaps we will make things easier on ourselves by sticking to these simple concepts. [reading]

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Most good tech references I have seen include a table defining the meaning of each symbol used. But I can appreciate the problem described. I do design of aircraft gears, and two of the primary tech references I use are the MMPDS metallic materials handbook and AGMA gear standards. MMPDS uses lower case alpha for CTE, and AGMA uses lower case alpha for pressure angle.
 
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I sympathize with the OP's complaint. Often the hardest part of reading a technical book or report is figuring out what the symbols represent. In this example it would be very bad practice to use the same symbol for two different things in one equation. However, that is not the case here. One N is italicized, but that is not very obvious. On the author's computer the fonts were probably more different.
A similar problem happens in posts on this forum where someone answers a question with an equation without defining the symbols. We all have to remember that the purpose of writing is to communicate ideas, not to put squiggles onto a screen.
 
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It is convention is physical sciences that units (Newton, N for example) are distinct from variable or parameters (Turn Rate, N for example) and therefore can co-exist side by side.
 
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Units of measure like Newton, Volt, Kelvin, etc, that are based on a person's name are proper nouns, and should be capitalized.
 
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Actually, not.

NIST Special Publication 330 2008 Edition said:
Unit names are normally printed in roman (upright) type, and they are treated like ordinary nouns. In English, the names of units start with a lower-case letter (even when the symbol for the unit begins with a capital letter), except at the beginning of a sentence or in capitalized material such as a title. In keeping with this rule, the correct spelling of the name of the unit with the symbol °C is “degree Celsius” (the unit degree begins with a lower-case d and the modifier Celsius begins with an upper-case C because it is a proper name).
Click to expand...

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homework forum: //faq731-376 forum1529
 
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@IRStuff
Am I crazy or is that conflicting?

First and Second sentences: "Unit names are normally printed in roman (upright) type, and they are treated like ordinary nouns. In English, the names of units start with a lower-case letter"
Third sentence: "In keeping with this rule, the correct spelling of the name of the unit with the symbol °C is “degree Celsius” (the unit degree begins with a lower-case d and the modifier Celsius begins with an upper-case C because it is a proper name)."

The third sentence would have us spell it Hz and Hertz. Per the second sentence, hertz would be Hz for the symbol and "hertz" in full. In fact, this trends with Kilohertz, and other multipliers, rather than KiloHertz.

I'm confused as to why the third sentence insists upon a capitalized Celsius, when referring to the unit, rather than the astronomer, then.

Edit-to-add: I suppose because "degree Celsius" is not a unit. "Degree" is a unit. "Celsius" is a 'modifier' per NIST, apparently. Nevermind - I should have thought it out more.
 
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Well that's asking for trouble, nm & nm - which is nanometers and which is Newton meters?

If only I had a copy of ANSI Y10.19/IEE-260 I might know.

Posting guidelines faq731-376 (probably not aimed specifically at you)
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No confusion; a newton-meter (N*m) is different than a nanometer (nm) per the SI usage guide. The two distinctions are the multiplication symbol between the newton and the meter, and the symbol for the newton is "N." THAT, at least, is pretty straightforward.

The degree-Celsius is unique in that it's the only SI unit that takes a proper name modifier, for apparently historical reasons, just like the base unit for mass is the kilogram, instead of the gram, for historical reasons.

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homework forum: //faq731-376 forum1529
 
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So per NIST spelt out they don't get abbreviated but when used as letter symbol it would appear the ones nominally named after people are capitals as opposed to lower case.

Which is what I thought we were talking about but now realize you were more specifically responding to tbuelna.


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