ISO 9001:2000 Section 7.6 d) states that measuring devices shall “be safeguarded from adjustments that would invalidate the measurement result.” I asked five different gage manufacturers at the Quality Exposition in Chicago this week about this requirement as it pertains to digital calipers and micrometers. Every gage salesman looked at me like I was the first person to ever ask the question and even though they understood my dilemma none of them had a satisfactory answer to my question.

My opinion is that every time an operator re-zeros their digital caliper they have just made an adjustment that could invalidate the measurement. I have seen plenty of digital equipment no longer reading zero when returned for calibration because of user adjustments. Even in the case where the caliper has an absolute scale, which reverts to the calibrated zero when it’s turned off and then on again, the absolute or origin reset button is completely assessable to the user on the face of the tool. There should never be any reason for any user to ever have to reset the absolute or origin on a digital tool. Why not put the button where it can’t be inappropriately or inadvertently pressed (like under the battery cover)? I need some feedback, do I just not get it or is there really an issue here?

The approach we took with digital calipers and micrometers in the testing lab I supervised was to have the operator's close them and zero them at the beginning of the turn, and then use a gauge block to verify them. Results were recorded in a logbook. Both calipers and micrometers were calibrated on a quarterly basis using a range of gauge blocks by me, the supervisor. If there were any problems during the turn, they were to rezero & re-verify. If that didn't work, they were to contact the lab tech ( a clerk type position) or the lab supervisor.

Had no problem with auditors comparing the lab system to the requirements of ISO 9001:1994, QS-9000, and ISO Guide 25 (the predeccessor to ISO Guide 17025).

Verifying measuring instruments on a regular basis is just good preventive practice - think :ca: - make it part of your work instructions, and you limit the amount of work you may need to do to identify and address potential non-conforming material if you recieve out-of-calibration instruments in for calibration. :)

My dilemma is what you have described, what everybody else I’ve talked to does, what most training video’s demonstrate, and most gage manufactures promote with their digital equipment is tantamount to having a user turn the barrel on their veneer micrometer because they think the zero is off a little. I don’t know anybody who would find that practice acceptable yet we accept it when it comes to digital equipment. I agree with having an operator verify their measuring equipment before each use but if it’s not reading correctly they should, in my mind, turn it in to be recalibrate. Most of the time, if it doesn’t read zero, it’s because there’s minute amounts of dirt on the measuring faces or natural variations in operator “feel” not because the gage needs to be reset. Yet we have an entire workforce trained to just hit the zero button, or worse yet, the origin button.

The key is not to disable the zero function but to train the top management and user on the concept of the science of measurement (metrology). If the calipers have been calibrated and there is no damage to the jaws when closed they will zero out without needing verification.

The zero function allows you to set your caliper, mic, or drop indicator at the nominal measurement value and check the plus or minus variance. Also if you follow down the same thought path what about dial indicators, pitch or thread mic, or height gages can be zeroed at a nominal measurement?

Before some one comments about this. In metrogaly a “gage” is device that makes a measurement and a “gauge” indicates pressure value.

Jeff

In metrogaly a “gage” is device that makes a measurement and a “gauge” indicates pressure value.

Jeff

Jeff:
Good advice about zeroing of instruments, but not so good on the English. Do you mean that "pressure value" is not the result of a measurement? "Gage" is a variant spelling of "gauge." The former is fine in informal contexts, but the latter should be used in formal writing. There is no special differentiation between the two in metrology--it would serve no purpose.

There are situations where "zero-ing" out the calipers can be beneficia for operators. If a .25 diameter hole is .75 from the edge of a part to the center of the hole, measure from edge of the hole to the edge of the part, zero out the calipers, move out .125 (half the hole) and zero again, now close the calipers and your reading should be .75

I have worked around allot of machinists that do this rather than pulling out the calculator or doing the math, it's not always as simple as my example so there are situations where it is a nice feature. Every person I have ever trained I have taught them to always close the calipers completely and zero out before taking any measurements.

Since I am also a machinist by trade I couldn’t agree more. I use the functions of a digital gage and the ability to zero it to do more complex measurements all the time and appreciate the capabilities it provides and in not having to use a calculator to do the math. That’s one of the reasons why I think digital gages with an absolute scale are so important. Whenever I turn my gage off and turn it back on it retains the absolute zero that was set during calibration. I wouldn’t want to loose the ability that the zeroing capability gives me in making measurements. But I wouldn’t re-zero the caliper before making any measurements. I may check my zero setting to see if anything has changed but I still depend on the absolute zero as my starting reference. The problem still exists however, that the absolute zero button is completely accessible and therefore not safeguarded against invalidating the calibration. If an auditor asks me how do I safeguard our digital calipers or micrometers against a user invalidating the calibration setting, I have no answer for them. Why haven’t any of the gage manufacturers been asked to address that issue. I still feel like I’m the only one who seems concerned about that as an issue. Am I missing something? Am I misinterpreting the intention of the standard? Has anybody else ever wrestled with this as an issue?

Do you know of a real-world instance where this has been a problem? In other words, have you ever been able to trace nonconforming conditions back to a spuriously-zeroed caliper? Do you even have strong suspicions that such a thing has happened? If so, then perhaps you need to switch to dial calipers, which are less likely to be tampered with. If not, then perhaps you should do some experimentation by calibrating a caliper, doing a GR&R, then re-zeroing it and doing another GR&R with the same parts and operators so that you have some actual data, rather than just possibly-groundless fear.

It doesn't matter if the calipers are digital or dial, you can fudge with the zero display. IMO it doesn't matter and the key is remembering what calibrating a pair of calipers is all about.

Our calibration procedure for calipers states:
Close the calipers, inspect the jaws for nice closure, if they have a gap or are not closing parallel then they need mechanical adjusting. If you open the calipers and measure a master block, are they within .001 (normally calipers are only accurate to .001). Repeat the measures for the inverse measuring jaws on top of the calipers. Do they get good inside and outside measures When used properly ? Yes or no determines if they are put back on the floor.

Those bold words are the key. The adjustment of setting a reference zero, digital or dial, does not change the accuracy of the calipers. It only changes the ret value based on method of measurement. The calipers are still calibrated accurately to operate within the set tolerance limits under proper use. The zero is reference to absolute zero, but digital calipers can be used properly as an incremental measuring instrument. If a caliper measures a 3.000 block as 3.000 from the closed state, it doesn't matter what the number on the screen says.

Example: If I set my calipers close at 1.000 and then measure a 3.000 block I would return value 4.000 which is a sign of a calibrated instrument (and possibly an uncalibrated person). Changin Zero does not change calibration! I think you don't have to worry about the zero button, I would argue that with an auditor all day and never back down.

As far as “Real World” issues I can only reference a Quality Digest article written way back in February of 1999. The article doesn’t go into depth about safeguarding equipment but it does point out the ease of which measurement errors can be introduced because of the zeroing capabilities of digital equipment. The link to the article is http://www.insidequality.wego.net/?v2_group=0&p=4499&ct=cdisplay&nt=true&cd_eid=233

It is important to remember the original issue in this thread and that is that ISO requires that measuring devices be safeguarded from adjustments that would invalidate the measurement result. I get the feeling that this is something nobody wants to talk about when it comes to digital equipment. Maybe an auditor will never question our practices but I wouldn't bet on that. I would like to be proactive and I would like gage manufacturers to address the dilemma.

I have never had an auditor ask. I've been doing this for about a dozen years and have worked with 4 different registrars.

As far as “Real World” issues I can only reference a Quality Digest article written way back in February of 1999. The article doesn’t go into depth about safeguarding equipment but it does point out the ease of which measurement errors can be introduced because of the zeroing capabilities of digital equipment. The link to the article is http://www.insidequality.wego.net/?v2_group=0&p=4499&ct=cdisplay&nt=true&cd_eid=233

The article, while providing useful information, does not reference any actual instances of nonconforming material that resulted from the issue at hand. It serves as a reminder that the potential problem should be addressed, I guess, but it's still theoretical. I've never known of an instance where zeroing a digital device caused problems.

It is important to remember the original issue in this thread and that is that ISO requires that measuring devices be safeguarded from adjustments that would invalidate the measurement result. I get the feeling that this is something nobody wants to talk about when it comes to digital equipment. Maybe an auditor will never question our practices but I wouldn't bet on that. I would like to be proactive and I would like gage manufacturers to address the dilemma.

It's maybe a bit much to expect that gage manufacturers would make significant (and costly) design changes if there's no ROI. In order to address your concerns vis a vis the standard, you need to have something in your system that addresses the concern. It's easy enough to demonstrate to an auditor that, A) it's not always possible to directly safeguard the device, and B) you've addressed the potential problem through requirements for recalibration when zeroing has the potential to create problems.

Just wanted to add a few things: AAMOROSO - I totally agree with everything you just said.

The zeroing button is there for a reason: use it if you know how to use it. You do not want to hide it or make it inaccessable. If you feel this is a problem with operators then teach them how to use the vernier and how to reset the zero.

If you want to make calipers (digital, dial, scale)tamper proof then here's what you do:
Put a few drops of white out on the adjusting screws of the gib. Loosening these screws to have a smoother feel along the whole length also changes the jaw pressure and how they close.
While white out won't totally stop people from adjustments it will show if someone has made an adjustment.
Adjusting these screws can change your measurements easily by about .005".

JSW05

Gee and all the years I have been using a ASME recognized term Gauge which is an instrument for measuring, testing, or registering pressure above atmospheric pressure and its incorrect English.

You would thank that when an organization like ASME who wrote a pressure gauge, oops gage standard B40.1 would only use those terms recognized in a Quality Dictionary.

Boy that causes my Hysteresis to have a big error, oops can't find Hysteresis in Quality Dictionary. Now what do I.....

Jeff

JSW05

Gee and all the years I have been using a ASME recognized term Gauge which is an instrument for measuring, testing, or registering pressure above atmospheric pressure and its incorrect English.

You would thank that when an organization like ASME who wrote a pressure gauge, oops gage standard B40.1 would only use those terms recognized in a Quality Dictionary.

Boy that causes my Hysteresis to have a big error, oops can't find Hysteresis in Quality Dictionary. Now what do I.....

Jeff

If ASME uses the spelling "gauge" to differentiate pressure-measuring devices from other types of measuring instruments and that spelling is understood in the context of some industry jargon, then I'd like to see where ASME makes the distinction. Just because ASME uses that spelling doesn't mean that they intend it to apply exclusively to a certain type of device.

Also, you shouldn't assume that English that's misused in the context of jargon should be considered universally understood. There has been some back-and-forth here regarding differentiating between "objectives" and "goals" when in fact the two are synonymous. Just because ISO 9000 talks about documenting "goals and objectives" doesn't mean that the meanings of the words have changed.

Just wanted to add a few things: AAMOROSO - I totally agree with everything you just said.

The zeroing button is there for a reason: use it if you know how to use it. You do not want to hide it or make it inaccessable....


That is exactly my point and if your training documentation clearly states that people using measuring instruments should be trained in the proper use of said instruments you are all set.

People can use a micrometer as "C clamp" and ruin calibration, how do you prevent that, TRAINING. In my opinion training someone how to properly use a mic or calipers is "safeguarding against adjustments that can affect the measurement to cause non conforming product."

According to Websters "Safeguard - a: a precautionary measure, stipulation, or device b : a technical contrivance to prevent accident"

Definition A is more applicable where as definition b is what you are referring.

If you removed the ability to adjust you may find it more trouble because then you are removing the ability to make an adjustment that is necessary to achieve a good measurement. You would find a hard time telling a Tool & Die Maker or Mold Maker that they cannot adjust the mics or calipers, there is not a quality expert in the world that would convince them that the rules are such. They would not argue with calibrating, in fact they would tell you I calibrate my tool every time I pick it up, the bi-annual calibration is to satisfy company records, the daily adjustments to the tool is to satisfy their desire for excellance.

I guess, if an auditor questioned us about this issue, I could reference ISO 10012-1, section 4.12, guidance, where it reads “The requirement for sealing does not apply to adjustment devices that are intended to be set by the user without the need for external references; for example, zero adjusters.” I could also put a written procedure in place stating how we handle digital gages with zero adjustments as an attempt to safeguard adjustments that would invalidate measurement results and train all our users on the procedure. I think that should (or would certainly have to) satisfy any auditor.

I still have a general concern with this issue and although I appreciate the feedback I’ve received on this forum I still think there is a big hole in our ability to safeguard measurement results when it comes to digital equipment. It seems to be a very touchy subject and most people I have talked to about it (and apparently even the standard itself) goes to great lengths to talk around the concern rather than address it directly. It’s these types of issues, however, that tend to come back and bite us down the road. Since digital devices have been around a long time now, our exposure must be limited or we would have had to address it before now. Perhaps it will come proactively in the near future as I have already seen a few digital pressure gages that have password protected calibration settings built into them.

I still have a general concern with this issue and although I appreciate the feedback I’ve received on this forum I still think there is a big hole in our ability to safeguard measurement results when it comes to digital equipment.
Let's get back to JSW05's question about "real world instances"; you referenced a magazine article. What we want to know is YOUR real world instances. What do you make? What digital equipment are you using? What is the skill level of the people using the digital equipment?

I talked to my Calibration Coordinator about the ISO 10012-1 guidance and he said he would interpret devices with “Zero Adjusters” as “the zero control on an analog meter when changing ranges” which makes perfect sense to me and makes my argument to an auditor very weak.

My real world experiences? I have a digital depth micrometer, which has a resolution of .00005 “and is used to inspect a feature with a .0012”, total tolerance. I had my doubts about the gage at first but I performed a measurement system analysis and found the device to be extremely accurate, repeatable and capable of the measurement in question. It far exceeded any veneer depth micrometer I had ever studied previously. The problem was in setting the zero during calibration. You literally had to “wring” the base to a lab grade surface plate and then bring the spindle gently into contact several times until you got repeatable zero readings. We found any amount of dirt or even oil could cause the readings to be off by as much as .0002” which would be the equivalent of 16% of our total tolerance and cause the system to no longer be valid. We trained all the users to never use the absolute zero setting capabilities of the device and told them if they had any question about the validity of their measurements to being it to the Metrology Lab to be checked. That worked in our situation and even when an operator inadvertently hit the absolute zero button he brought it into the Lab to be reset. However, since the button is exposed it isn’t “safeguarded” and if an operator didn’t recognize they accidentally hit the button all of the resulting measurements would be invalid, including those of the following shifts. It would go completely unnoticed. Did it ever happen? Not to my knowledge but it meant constantly enforcing the procedure with the operators and whenever possible it is better to take that responsibility out of their hands.

Other examples have come from equipment returned for calibration that, when the anvils are cleaned don’t read zero anymore. By as much as .002” in some cases which then caused us to have to investigate the potential for nonconforming material. Which is a nightmare unto itself. Of course I’ve also seen dial calipers returned with the bezel lock unlocked and the bezel free to rotate as you handled the device.

If you were to do an FMEA on a digital Caliper and listed one of the Potential Failure Modes as “invalid zero adjustment” and Potential Effect of Failure as “invalid measurement result” what RPN would you have? I came up with 160, which in our system would warrant a recommended action. About the only thing I could realistically reduce would be occurrence and detection. I can perform training to reduce the occurrence but I would argue that training is not an effective action to address root cause, and it would only have a minimal effect on the resulting RPN. That leaves me with detection, which means design control by removing the potential of an operator inadvertently zeroing the device and invalidating the measurement result.

All I’m asking for is to put the absolute button under the battery cover so it can’t be accidentally hit or provide a menu option with a password protect. Then it is truly “safeguarded.” I still get the feeling like I'm the only one who feels this is an issue. Doesn't anybody else out there see it as an issue?

I talked to my Calibration Coordinator about the ISO 10012-1 guidance and he said he would interpret devices with “Zero Adjusters” as “the zero control on an analog meter when changing ranges” which makes perfect sense to me and makes my argument to an auditor very weak.
Your hypothetical argument. Not to say that there's no value in anticipation, but you shouldn't wear yourself out on the argument before it happens.

My real world experiences? I have a digital depth micrometer, which has a resolution of .00005 “and is used to inspect a feature with a .0012”, total tolerance. I had my doubts about the gage at first but I performed a measurement system analysis and found the device to be extremely accurate, repeatable and capable of the measurement in question. It far exceeded any veneer depth micrometer I had ever studied previously. The problem was in setting the zero during calibration. You literally had to “wring” the base to a lab grade surface plate and then bring the spindle gently into contact several times until you got repeatable zero readings. We found any amount of dirt or even oil could cause the readings to be off by as much as .0002” which would be the equivalent of 16% of our total tolerance and cause the system to no longer be valid.
It sounds like a tradeoff question. Do the disadvantages of the digital gage mean that using the analog/vernier type would be more advantageous in the end, all things considered?

Other examples have come from equipment returned for calibration that, when the anvils are cleaned don’t read zero anymore. By as much as .002” in some cases which then caused us to have to investigate the potential for nonconforming material.
An error of .002" shouldn't be limited to just digital gages. If there's some junk on the anvils that's .002" across, it's going to be measured regardless.

If you were to do an FMEA on a digital Caliper and listed one of the Potential Failure Modes as “invalid zero adjustment” and Potential Effect of Failure as “invalid measurement result” what RPN would you have? I came up with 160, which in our system would warrant a recommended action.
First, it's not a good idea to set "trigger" RPN values. When the "trigger" is say, 150, the highest RPNs you're likely to see will be in the 140's. Also, assignment of RPN factors is almost always subjective. Remember also that they're called recommended actions, not mandatory actions. The expectation is that you'll review the situation for reasonable ways to mitigate risk. It doesn't mean that you must do something that will lower the RPN (hence the risk).

About the only thing I could realistically reduce would be occurrence and detection. I can perform training to reduce the occurrence but I would argue that training is not an effective action to address root cause, and it would only have a minimal effect on the resulting RPN. That leaves me with detection, which means design control by removing the potential of an operator inadvertently zeroing the device and invalidating the measurement result.
It seems to me that in your FMEA surmisal that you haven't identified the root cause. Maybe the root cause is "Digital gage used instead of analog." You also seem to be confused about "detection" as it's used in the FMEA context. In this instance it would refer to the relative likelihood of detecting the problem before an "invalid measurement result" occurs.
All I’m asking for is to put the absolute button under the battery cover so it can’t be accidentally hit or provide a menu option with a password protect. Then it is truly “safeguarded.” I still get the feeling like I'm the only one who feels this is an issue. Doesn't anybody else out there see it as an issue?
It's a matter of priorities, I suppose. I have a tendency to not worry much about things that I can't control. I think you've identified a valid issue, but short of banishing digital devices from your workplace, there isn't much you can do that you haven't already (admirably) done.

If an operator inadvertantly sets the zero on his calipers and makes bad product that goes unoticed until the next operation or worse shipped to a customer our NCP procedure would activate an investigation. If it could be determined that the operator used the instrument incorrectly, the corrective action procedure would kick in and the corrective action would state training in proper use of measuring instruments is required.

I would never say that Starret tools or Brown & Sharpe or any others make a product which is faulty or not acceptable. To remove adjustability from a measuring tool you would have to have solid measuring for everything you measure. There is nothing stopping someone from using a tool incorrectly other than training. If your operators do not understand how to use a pair of calipers properly train them or take the calipers away.

...the corrective action procedure would kick in and the corrective action would state training in proper use of measuring instruments is required.

But you would probably have a job description that would include the need for the operator to be able to use the tools of the trade, no? So maybe the root cause goes a bit deeper.

But you would probably have a job description that would include the need for the operator to be able to use the tools of the trade, no? So maybe the root cause goes a bit deeper.

Absolutley JSW05,

If you go back into my previous posts, I have preached that proper training is safeguarding against bad adjustments of the calipers. :agree1:

Hehe - here is my 2 cents since I've been calibrating mechanical tools since 1975:

There is a difference between mechanical and electronic gages. In the mechanical world, we have a mechanical zero that is typically set at 3 points on a vernier micrometer for example. Once we have these 3 zero points set, we can then begin calibration. Once the vernier gage is calibrated and leaves our lab, the operators will usually call us to verify the gage since it no longer indicates a mechanical zero (they do not have the wrench necessary to make changes on the barrel). Usually the deviation from zero is the result of debris on the anvil surfaces. Once we show the operators that they need to wipe the anvils to check, they can see that the zero returns to it's original position. This mechanical zero remains accurate as long as the micrometer is not dropped or used as a C-clamp. This is the way it was 15-20 years ago.

Today with digital gages, you are no longer setting a mechanical zero, but instead a electronic one that can be set anywhere on the gage. We no longer get calls to verify gages because it's done by the operator, who might rezero the gage with debris on the anvils; thus, preventing an accurate measurement. I agree that training plays a very important part, but I guess I'm from the old school - I trust the ability of mechanical gages more readily than electronic.

JSW05

Gee and all the years I have been using a ASME recognized term Gauge which is an instrument for measuring, testing, or registering pressure above atmospheric pressure and its incorrect English.

You would thank that when an organization like ASME who wrote a pressure gauge, oops gage standard B40.1 would only use those terms recognized in a Quality Dictionary.

Boy that causes my Hysteresis to have a big error, oops can't find Hysteresis in Quality Dictionary. Now what do I.....

Jeff

Gauge, as in Gauge Pressure (psig) is referenced to atmospheric pressure. It is the most common type of pressure gauge, as opposed to an Absolute Pressure Gauge (psia), which is referenced to absolute zero (a perfect vacuum).

Now, none of this has anything to do with whether someone spells the measuring device Gauge or Gage. Gage is simply a commonly used variant spelling of gauge, which is the proper term. It is akin to spelling through as thru - technically it is incorrect, but so common that it is the norm (in the USA that is).

At a previous company that I worked for, we applied sealing wax to the gib stop screws on calipers. If the gib stop screws work loose and allow the gib to move, this can affect the accuracy of the gage.
Another example of this is with snap gages. After the dimension is set, some kind of sealer should be put on the adjustment screws so they don't come loose and allow the anvils to move.
For mics, you may want to plug the thimble adjustment hole and remove the little tool (from operator access) that is used for making that adjustment.
Just some food for thought.
~Jane