Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


position vs true position - just semantics?

position vs true position - just semantics?

position vs true position - just semantics?

Everyone at my work who "knows" GD&T from learning it at their old job refers to position, incorrectly, as true position. I think this misuse of terms happens pretty frequently throughout industry. Is it worth fighting the good fight to try to have the people at my work refer to the terms correctly knowing full well that any time they speak with anyone outside of our organization that other person will most likely be using these terms incorrectly anyways?

I have found that if someone was confusing RAME with UAME and you set them straight on the definitions they would probably thank you for the clarification. But when you tell them the actual definitions of position and true position they tend to dismiss it.

Am I the only stickler for correct usage of terms? To me it is nails on a chalkboard every time I hear position called true position.

Also, how come no one incorrectly refers to profile as true profile? At least be consistent with you incorrect use of terms.

RE: position vs true position - just semantics?

In the end, it is pretty much semantics. The standard says that "true position" is the perfect location. The symbol then provides a tolerance around this perfect location.

When teaching a GD&T class, I make a point of this distinction, and try to get everyone to call the tolerance the "position" symbol. But in your everyday job, I wouldn't make an issue out of it.

For those who might really insist on calling it the true position symbol, one strategy you can use is to ask them why they don't call flatness the "true flatness" symbol (or true perpendicularity, or whatever).

One popular textbook used to refer to position as TOP, or "tolerance of position." Not wrong in itself, but I say just stick to the terms used in the standard. I think in the newer editions he's backed off from using that acronym.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

RE: position vs true position - just semantics?

It's like trying to get people to stop using the term 'GD&T' as a shortcut to mean feature control frame** or just Dimensioning and Tolerancing. "Geometric Dimensioning" isn't defined in the standard; certainly it isn't the title of any version of the 'Y14.5 standard, and was only mentioned as (somehow) being different (it isn't) from coordinate dimensioning in the '1994 and some earlier versions.

I blame Foster for his 'Geometrics...' books and early, non-standard works like Foster's 1963 Honeywell book "A Treatise on Geometric and Positional Dimensioning and Tolerancing."

Slang is a tough thing to stamp out.

**As in the phrase 'put some GD&T on the drawing.' Such drawings already have dimensions and direct tolerances, so the only thing it could mean is to add feature control frames and maybe datum symbols. Hence FCF == GD&T.

RE: position vs true position - just semantics?

IMHO there is absolutely nothing wrong about using convenient abbreviation that everybody understands.

For example, the International Organization for Standardization is using the short form ISO even though it is not correct abbreviation in any official ISO language.

The story usually associated with that is that the short form ISO is not an acronym, but rather, a word derived from the Greek isos, meaning “equal.”

Now, if you ask 100 people what ISO is, 90 of them are probably unaware about “Greek” origin of the word. Nevertheless the term is universally accepted and understood in 200-something ISO member countries (and they don’t bother to create their own local abbreviations, just call it ISO anywhere from Greece to Russia to China)

Similarly, abbreviation GD&T, even if not defined as a term in latest version of the standard, is universally accepted and understood.

It still used by biggest names in the industry, including, but not limited to (in no particular order):

Alex Krulikowski: http://www.amazon.com/Fundamentals-Geometric-Dimen...

David P. Madsen: http://www.amazon.com/Geometric-Dimensioning-Toler...

James D. Meadows: http://www.amazon.com/Geometric-Dimensioning-Toler...

Bruce A. Wilson: http://www.amazon.com/GD-Application-Interpretatio...

Gene Cogorno: http://www.amazon.com/Geometric-Dimensioning-Toler...

Robert H. Nickolaisen: http://www.amazon.com/Certification-Geometric-Dime...

Georg Henzold: http://www.amazon.com/Geometrical-Dimensioning-Tol...

And many others who I hope will forgive me for not mentioning their names.

It is also interesting to note that J. D. Meadows uses term “Geometric product definition”, and G. Henzold uses “Geometrical properties”, so one may say, GD&T should be generally understood as “Dimensioning and tolerancing of geometrical features”.

I really don’t mean to sound rude, but my personal idea would be: just let it go.

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

RE: position vs true position - just semantics?

I agree with J-P that using 'true position' instead of 'position' isn't a huge problem in the end. At my workplace when people mean 'position tolerance' they almost always use 'true position'. And even though I don't like it, I have never witnessed any miscommunication or quality issues because of that. It is definitely a good thing to make them aware that they use incorrect terms, but is it something worth fighting for?... I am not sure.

On the other hand, I have occasionally experienced serious issues caused by improper use of term 'datum' instead of 'datum feature'. From my experience some people that say 'datum' (when they really mean 'datum feature') tend to incorrectly think that relationships between datum features don't have be controlled on the drawing because by definition these features are perfect to each other. It takes some time to explain them that they are wrong. Not to mention it costs money to fix the drawings missing these extremely important relationships.

Another example along the same lines that I can think of is 'squareness' vs. 'perpendicularity'. Perhaps for English speaking people this is clear/obvious, but I can recall at least a couple situations when a non-English speaking person had a really hard time to figure out what the 'squareness' really is in GD&T vocabulary (pardon me, Dave - in D&T vocabulary upsidedown). Especially that this term has no official definition in the standard.

RE: position vs true position - just semantics?

Since we're into word play in this thread, do you all prefer the adjective "diametric," "diametrical," or "diametral"? (This is in the context of describing a cylindrical tolerance zone around an axis.) A certain OEM around here uses the last one, and I refuse to say it. tongue

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

RE: position vs true position - just semantics?

I'd simply be grateful that a simple terminology quirk is the forefront in my list of problems with coworkers' understanding of the topic.

RE: position vs true position - just semantics?

My approach is: clarify the distinction when appropriate, like in the classroom. Otherwise, don't go on a stamp-it-out campaign.

Certified Sr. GD&T Professional

RE: position vs true position - just semantics?

When this happens, usually with details other than GD&T, I simply use the correct words in my daily conversations. People often catch on or come right out and ask me. They're usually using the wrong word only because they heard it from somebody else.

RE: position vs true position - just semantics?

Current ASME Y14.5 is titled, "Dimensioning and Tolerancing". Section 7 is titled, "Tolerances of Location". Subsection 7.2 is titled, "Positional Tolerancing". So there you go.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close