The Logic behind Tolerance vs. Least Count 1/10 Ratio

S

sarasheed

#1
This is a good old doubt. What is the logic behind useing a measuring Instrument whose least count is 1/10 of the tolerance of item to be measured? Why not 1/3 or 1/4 as many people recommend?
Is there any standard to justify either of the above cases ?

sarasheed.
 
Elsmar Forum Sponsor

Bev D

Heretical Statistician
Staff member
Super Moderator
#2
Re: The logic behind Tolerance vs. Least Count 10:1 Ratio

basically it comes down to what you want to do with the data and how many false rejections you are willing to tolerate.

when you use a gage that is only 1/4 to 1/3 of the tolerance then you essentially have only 3 to 4 possible results. This is essentially ordinal data. Standard deviation calcualtions will be overinflated so you woudl need to treat the results as 'attributes' data (pass / fail or categorical data)

depending on the criticality of the characteristic either choice may be viable.
 

BradM

Staff member
Admin
#3
Re: The logic behind Tolerance vs. Least Count 10:1 Ratio

A[art from Bev's good explanation, here is a paper that Transcat offers from their website on the subject. The graphs may help visual understanding.
 

Attachments

D

Duke Okes

#4
Re: The logic behind Tolerance vs. Least Count 10:1 Ratio

I believe an old standard such as 45208 or 45662 required a minimum of 1/4, but that obviously gives a higher level of measurement uncertainty.
 
Last edited by a moderator:

Stijloor

Staff member
Super Moderator
#5
Re: The logic behind Tolerance vs. Least Count 10:1 Ratio

This is a good old doubt. What is the logic behind useing a measuring Instrument whose least count is 1/10 of the tolerance of item to be measured? Why not 1/3 or 1/4 as many people recommend?
Is there any standard to justify either of the above cases ?

sarasheed.
Hello sarasheed,

Here is a very simple, non statistical example that I use when teaching metrology.

Using the metric system (based on the factor "10") as an example:
  • When you're measuring whole millimeters (mm), you want the variations to visible in in 1/10th (0.1) of the values.
  • When you're measuring in 0.1 of a mm, you want the variations to be visible in 0.01.
  • When you're measuring in 0.01 of a mm, you want the variations to be visible in 0.001.
Hope this helps.

Stijloor.
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#6
This is a good old doubt. What is the logic behind useing a measuring Instrument whose least count is 1/10 of the tolerance of item to be measured? Why not 1/3 or 1/4 as many people recommend?
Is there any standard to justify either of the above cases ?

sarasheed.
One more point: I wouldn't use a "standard" as justification for anything. Good statistical and engineering knowledge shodul be combined with practical knowledge of the characterstic and it's design/use intent to determine how much resolution is necessarry for the measurement system.

As I've said before, there is no substitute for good old fashioned thinking. A standard or a rule of thumb or someone's random suggestion is no substitute for knowing what one is doing. The world is not comprised of 'cookbook' solutions.
 

Jim Wynne

Staff member
Admin
#7
One more point: I wouldn't use a "standard" as justification for anything. Good statistical and engineering knowledge shodul be combined with practical knowledge of the characterstic and it's design/use intent to determine how much resolution is necessarry for the measurement system.

As I've said before, there is no substitute for good old fashioned thinking. A standard or a rule of thumb or someone's random suggestion is no substitute for knowing what one is doing. The world is not comprised of 'cookbook' solutions.
Exactly.:agree1: With each instance of a need for measurement, a decision has to be made with regard to resolution of the results. Sometimes 10:1 might be overkill, and sometimes it might not be enough. It's a matter of understanding variation, and what you need to know about it.
 
D

Duke Okes

#8
Standards for what color the lights should be for stop, caution and go are quite useful, as are how to design electrical outlets. So while standards do not always apply to every situation, they greatly reduce the amount of variation we have to deal with. After all, specifications are standards, just not necessarily developed by a standards body (although in the case of types of steel, aluminum, etc. they are).
 

Jim Wynne

Staff member
Admin
#9
Standards for what color the lights should be for stop, caution and go are quite useful, as are how to design electrical outlets. So while standards do not always apply to every situation, they greatly reduce the amount of variation we have to deal with. After all, specifications are standards, just not necessarily developed by a standards body (although in the case of types of steel, aluminum, etc. they are).
I don't think anyone is saying that standards aren't useful and needed in some instances, but we need to differentiate between vague rules of thumb with uncertain provenance and actual standards.
 

Bev D

Heretical Statistician
Staff member
Super Moderator
#10
Standards for what color the lights should be for stop, caution and go are quite useful, as are how to design electrical outlets. So while standards do not always apply to every situation, they greatly reduce the amount of variation we have to deal with. After all, specifications are standards, just not necessarily developed by a standards body (although in the case of types of steel, aluminum, etc. they are).
Of course the types of standards you reference are useful and in many cases very desired.
However, your examples are not the same as the type of 'standard' that was meant. I thought I was fairly clear that my reference to a standard was limited to the OP's use in his question: wanting to know if their was a standard to justify the use of a 1/4 or 1/3 resolution of a measurement system.

The two standards you mentioned that might justify a 1/4 resolution are decades old and come from a time when computers rare or at least not commonly used and analyses were done by hand...they have both been primarily superceded, one by ISO9000.

:caution:WARNING: WHAT FOLLOWS IS A RANT. IT IS NOT FIRED DIRECTLY AT THE POSTER QUOTED ABOVE BUT TO BE A GENERAL STATEMENT THAT WILL NO DOUBT TAKE THIS POST OFF TOPIC.:mad:

However, my concern is not the age of these standards but my original statement regarding using logic and reason to determine the resolution that will be useful given the application. Just because a standard says so, doesn't mean it's true.

In general I am more concerned that the quality profession has moved further from thinking and closer to a simple "if a standard or my Customer says I have to do this to comply, or if I can get a standard to justify my lack of thoughtful input or learning that's what I'll do and no more."

Have we all lost our collective minds?

Many on this forum provide - or attempt mightily to provide - thoughful input to questions posted here. the input is meant to teach, learn, explore, reason and hopfully in the end raise the collective usefullness of all who come here.

Now I know that I am most likely merely annoyed by some of the recent posts that seem to have been looking for "agreement" statements to "prove" their point as if we can vote to change the laws of physics; or even the less benign but far more troubling "I've just appointed to implement SPC, or Capability studies or FMEA or whatever and I have no idea how to do this or what it means". I feel for these posters. Their managment has essentially said "this is a requirement; someone has to ensure that we comply to it and I picked you". There is no concern about doing the right thing; only about doing what is necessarry to comply. These situations simply tarnish our profession. Blind compliance to a requirement does not provide quality. But it seems more and more that this is all we have time to do. The proliferation of 'standards' that dictate exactly how to apply quality are obviating our need to think and reason and improve. (my sincere apologies to those who just blew their morning coffee thru their noses; that must have hurt! and for those who are firing up to tell me how useful ISO or AS or whatever is, let me say now that I agree that standards have usefullness; just not when all logic and reason are suspended in their application and execution)

I would refer to Bert Gunter's "Final Fusillade" in his Statistics Corner column for the April 1998 issue of Quality Progress. He states it much more eloquently than I ever could:

"What is the state of the quality profession today? In a word, deplorable. I am frankly dismayed by what I believe has been a retreat from the activism and professionalism of 10 years ago to what seems to me to be a return to the bad old days of passive checking of conformance to rules...This
is all form and no substance, much like the old (and superseded, I hope) military procedures that required 30 pages of documentation to assure that off-theshelf commercial underwear met requirements."

Well, I guess that about does it. I'm going to hit "submit reply" before I lose my nerve
 
Thread starter Similar threads Forum Replies Date
S Logic behind signal detection in attribute GRR% calculation Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 2
K EU MDR Rule 11 - Does the 'Risk logic' used in Rule 11 conflict with that used in the other rules? EU Medical Device Regulations 2
T Logic that determines what production testing is needed ISO 13485:2016 - Medical Device Quality Management Systems 2
T Has anyone considered what logic is? Coffee Break and Water Cooler Discussions 23
M The logic around Takt Time Lean in Manufacturing and Service Industries 7
I PLC (Programmable Logic Controller) Qualification Requirements Qualification and Validation (including 21 CFR Part 11) 11
8 Single Piece Flow Game - Understanding the Principles and Logic of Single Piece Flow Lean in Manufacturing and Service Industries 3
C Try this site - Logic puzzles Brain Teasers and Puzzles 0
A Logic riddle Brain Teasers and Puzzles 4
M Fuzzy Logic - Real or Not? Hot or Not? Statistical Analysis Tools, Techniques and SPC 9
B Definition Error Proofing vs. Programmable Logic Controls (PLCs) Definitions, Acronyms, Abbreviations and Interpretations Listed Alphabetically 1
G The GUM (Guide of Expression of the Uncertainty) against the logic (?) - Acoustical Measurement Uncertainty (MU) 6
P CE Marking EN ISO 13849-1: Electrical Panel behind interlocked doors CE Marking (Conformité Européene) / CB Scheme 9
M QMS standard behind / under VDA? VDA Standards - Germany's Automotive Standards 7
U Theory and Practice Behind Expecting a Distribution for my Data (specially the normal Statistical Analysis Tools, Techniques and SPC 48
R Mathematics behind GRP kijima type 1 Reliability Analysis - Predictions, Testing and Standards 2
G Structure and Method behind the Planning of 8.2.2 Internal Audit Internal Auditing 6
Marc FDA: Software Failure Behind 24% of Last Year's Medical Device Recalls Other Medical Device and Orthopedic Related Topics 2
B What is the psychology behind three rings? Customer Complaints 8
K Seeking help in making a decision - Project behind schedule Quality Manager and Management Related Issues 11
M Practical Reasons Behind The ISO 13485/QSR Regulations ISO 13485:2016 - Medical Device Quality Management Systems 6
Jen Kirley Puppies Behind Bars Coffee Break and Water Cooler Discussions 8
Y Identifying measurable processes: How not to lose the forest behind the trees? ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 4
B Algebra behind variance in Gauge R&R Using Minitab Software 5
M AS9100 Audit Coming up and We are Behind in a Few Areas! AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 7
D Consultant's Dilemma - Implementation project is behind schedule Consultants and Consulting 16
N Can the person behind ISO Certification also be the Internal Auditor? General Auditing Discussions 13
ScottK Can someone explain the marketing behind this ad? Coffee Break and Water Cooler Discussions 21
Marc What's Behind Customer Satisfaction Awards? J.D. Power 'Cozy' with "Winners" World News 4
B Sampling Questions - Theory behind the use of sampling techniques Inspection, Prints (Drawings), Testing, Sampling and Related Topics 4
Y ISO/TS 16949 - What is the meaning behind this number? IATF 16949 - Automotive Quality Systems Standard 7
A Avoiding ISO 9000 Registration - Hiding behind 'Customer Wishes' ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 12
D Tolerance symbol Inspection, Prints (Drawings), Testing, Sampling and Related Topics 8
D Calibration tolerance question using Pipettes Medical Device and FDA Regulations and Standards News 1
M Determining a tolerance value for Measuring devices in-house inspection General Measurement Device and Calibration Topics 12
G 0.00005" tolerance on micrometer with 0.0005" resolution? General Measurement Device and Calibration Topics 4
N Drawing tolerance vs. Measurement device General Measurement Device and Calibration Topics 7
I Control Plan (Product/Process specification/ Tolerance) acceptance FMEA and Control Plans 27
J Mechanical inspection techniques of close tolerance parts Inspection, Prints (Drawings), Testing, Sampling and Related Topics 4
Proud Liberal Small radius with tight tolerance on a torus General Measurement Device and Calibration Topics 4
L GRR for a tolerance that has changed Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 6
T How to justify this High %Tolerance Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
D Tolerance definition based on expected Cp/cpk Reliability Analysis - Predictions, Testing and Standards 14
N % Tolerance - Type 1 study on the gages, then a gage R&R (ANOVA) Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 4
S Tolerance limits for micro balance General Measurement Device and Calibration Topics 1
J Determining SPC tolerance Statistical Analysis Tools, Techniques and SPC 21
Q % Study variation low, % tolerance high - GR&R Interpretation help Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 3
R Uncertainty in measurement larger than tolerance Measurement Uncertainty (MU) 2
WEAVER Electronic Weighing Scale Calibration Tolerance Manufacturing and Related Processes 1
I Determining Calibration Tolerance of a Measurement Device General Measurement Device and Calibration Topics 2

Similar threads

Top Bottom