If you have a gage that you use seldom to rarely (1-6 times) during a calibration cycle (which is typically one year), do you still get it calibrated? It seems like a large waste of time and money to calibrate/verify a piece of equipment that is hardly used.

EXAMPLE: We use 2 dial indicators in the production area (tooling department and machine maintainance) and 1 that we use in the "lab" with our height indicators. I sent them out annually as needed. We have 6-8 dial indicators total. We only use the other 3-5 indicator as substitutes while the normal ones are sent out for calibration. Does 1 week's worth of use justify calibrating these "extra" gages every year?
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I have seen plenty of good ideas/programs posted here like placing a rarely used gage in a sealed bag after calibration. If unopened, the following calibration just involves a new sticker. How does this work if you can't physically seal it?
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Other people simply mark "do not use until calibarted". This really only works if you can calibrate it in-house and/or don't need it in a rush. I've done this on a few attribute and go-nogo gages which are currently not needed (semi-obsolete product line).
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Any tips/comments on whether or not I should calibrate rarely/never used gages or simple extending the calibration cycle time.

(I've only been Quality Manager for 1 year and I'm about to send out gages again that have not been used or rarely used in one year).

Thanks Bob M

Bob:

To me this is a judgement call, depending on expected usage. If you have a gage that has not been used and you do not anticipating needing it, I would mark it "do not use until calibrated".

For gages that see little use, but when needed are needed immediately and cannot be calibrated in house, they should be sent out to be calibrated, IMO. The reason is that over a year, a measuring device can be jostled, and it would be subject to dust, humidity and heat/cool cycles.

You might check with the manufacturer to see what they say about calibration.

Hope this helps.

Craig

One option you can consider is extending the calibration cycle on the gages that aren't being used often, as long as they are staying within specs each time they are calibrated. Some people are comfortable with this and some aren't, but it is something to consider.

Bob:

To me this is a judgement call, etc.

I also assumed that those that can not be calibrated in house should TYPICALLY be sent out as scheduled.

The seldom used gages are already stored in a cabinet in our semi-climate controlled quality lab (same heat/air system as the office). So jostling and major temperature changes are not a major problem.

Most of our seldom equipment includes - Height Gage, Height Master, dial and test indicators, extra micrometers, old or obsolete go-nogo, old or obsolete part specific gages, even our surface plate is hardly used except for gage calibration and occasional part verfication.

I'm not talking about saving the company alot of money, but I'm just looking for options/ideas. On the surface it seems crazy to annually pay to verify a gage you have used 2-3 times, just because you have a "calibration program".

I probably will send most of the stuff out, but I'm just looking for other people opinions and how they work with this situation.

One option you can consider is extending the calibration cycle on the gages that aren't being used often, as long as they are staying within specs each time they are calibrated. Some people are comfortable with this and some aren't, but it is something to consider.

I am considering this on a few.
12 months vs. 18
1 year vs. 2 years

Is it OK for US to set our own frequency on seldom used equipment?

Is it OK for US to set our own frequency on seldom used equipment?

Yes it is. Check the history on the gages to make sure that they have been within the specs and then you can push them out. Make sure to track them and make sure they stay within during the longer period though.

Bob,

I just went through this myself. The "status quo" around here was to calibrate our dial calipers on a monthly basis. I just changed it to quarterly based on historical review. We rarely found an out of tolerance condition at calibration. If there was a problem with the gage, the operator would find it long before it was due for calibration.

I have a set of angle blocks that are used once per year for checking our protractors. I set the calibration frequency for 5 years.

JMHO, as always.

CarolX

Bob,

I just went through this myself. The "status quo" around here was to calibrate our dial calipers on a monthly basis. I just changed it to quarterly based on historical review. We rarely found an out of tolerance condition at calibration. If there was a problem with the gage, the operator would find it long before it was due for calibration.

I have a set of angle blocks that are used once per year for checking our protractors. I set the calibration frequency for 5 years.

JMHO, as always.

CarolX

Monthly? Wow!

I like that idea for angle blocks and similar... I should check to see if anyone is using ours in the tooling department...

Bob,

I just went through this myself. The "status quo" around here was to calibrate our dial calipers on a monthly basis. I just changed it to quarterly based on historical review.

Exactly,

The calibration period should reflect the calibration results... A while back we had to go in the opposite direction and put a number of micrometers on a monthly schedule due to increased use. The calibration results made it blindingly clear that the previous three month cycle was to long.

On the other hand, if the results stay well within the limits every time the period could (or rather should) be extended. To calibrate too often serves no useful purpouse, and not doing it often enough may of course be a lot worse.

Calibration prior to use is a good option when it comes to infrequently used equipment, because we are well adviced to consider that equipment can slip out of tolerances without being removed from its box... It's rare, but it happens.

Good thread here....

/Claes

Based on some of the replays to your question about interval cycle for devices that are not use often, extenting cycle, and other options are valid. The main focus should be the application of use for the device.

A micrometer typical accuracy is ±0.001. If the application of use of the device being measured requires the values to of acceptance has a tolerance of ±0.005 you then have a 5:1 Ratio. The micrometer then could experiece a out of tolerance condition as high as 400% without causing a problem.

Look at the accuracy of the measuring standard, (your device) use to measure your product. find out what the ratio relationship is, then you can make informed decisions related to use, cycle and other conditions.

Everyone:
Help me understand what you mean by "calibrate" as opposed to "certify" or "zero out" and also how you relate any of these terms to Gage R & R (MSA)

As I read posts here and in ASQ's Forums, there seems to be a lot of interchangeability of terms far different from my understanding and experience over the last 25 years.

I have hundreds of horror stories about operator-owned personal micrometers which have never, ever been included in organization calibration or certification processes. (Also scary stories about organization-owned instruments.) One guy used his two-inch micrometer to "gently" crack walnuts so the meat wouldn't shatter. Other guys used to crank the micrometer down so hard the anvils left dents in the material (mechanical advantage of a screw is amazing!)

Everyone:
Help me understand what you mean by "calibrate" as opposed to "certify" or "zero out" and also how you relate any of these terms to Gage R & R (MSA)

Wes,
You are correct....and for as long as I have been in the quality field..the term "calibrate" has actually meant "to check". Calibration is the adjustment you make for an out of tolerance condition. But to make things as easy as possible in the worlds we work in...I think we all refer to the function as "Calibration".
Right or wrong....IMHO it is just semantics. As long as the message is understood.

CarolX

If that is the case, then last week I calibrated my engine oil, I calibrated my blood pressure, and I even calibrated the caliber of my calipers.

Seriously though, if the AIAG is still a credible authority, it defines calibration in its Measurement Systems Analysis (MSA) manual as "comparison to acceptable standards", and in QS-9000 as "a set of operations which compare values taken... to a known standard". So, indeed, "checking" is a valid synonym. Although I too tend to think of calibration as the act of bringing a device back to nominal.

One method we have used for seldom used gages is to use different interval types. We use the standard "flat" time where a gage is due 91 days after the calibration date, the normal interval type. We also use "issue" time where calibration time only counts when gages are in use. If they are sitting in a drawer in the tool crib, the time isn't counting. We also have the capability of counting every use of a gage.
We currently have a computer system to track calibrations, but years ago we did the same thing with cards.

Bob,

Can't you rotate your gages and put them on rotating calibration cycles?

In our testing lab, we state that items requiring calibration that are seldon used, are taged and placed in the equipment cabinet and calibrated prior to use. For us, calibration is much more expensive ($500).

On the same note, out side of the test lab, we do our own calibrations including company and employee owned. Only our master gages are sent out for calibration.

Is it worth your efforts to purchase the necessary equipment to perform calibrations yourself?

Cindy

One method we have used for seldom used gages is to use different interval types. We use the standard "flat" time where a gage is due 91 days after the calibration date, the normal interval type. We also use "issue" time where calibration time only counts when gages are in use. If they are sitting in a drawer in the tool crib, the time isn't counting. We also have the capability of counting every use of a gage.
We currently have a computer system to track calibrations, but years ago we did the same thing with cards.
Hi Charles and Welcome to the Cove:bigwave:

What a great idea. How difficult was it to manage in the card system?

CarolX

It was not difficult to manage in the card system. It just took a a little extra work. The cards were like the old library cards, we used 4 x 6 index cards. The crib attendant would write on the card were the gage was being issued to and the date, and when it was returned they would manually subtract the days it was out and mark a running balance on the card. When the balance got within 10 days the gage was issued to calibration.

If I were in your position I would look at a calibration cycle based on usage. This is an accepted criteria for setting a cycle time. In doing this you might find that the seldom used gages only need calibration once every 2-3 years.

Why don't you consider extending the outside calibration interval on your seldom used gages and verify them internally between calibrations?

You could perform those, say, every three or four months. That way you would know the gages are still in tolerance during storage and are ready to go when needed.

What would you do if you extended the outside calibration intervals to 18 months and during the 17th month you needed to use the gage only to find the batteries are dead (if used) or the gage is unusable?

Not an ideal situation...

Golly, Ken. I guess the rest of us don't think of batteries when we think of calibration. A change of batteries doesn't change calibration of any dimension measuring instrument. A weak battery might make a big difference in items like continuity testers, voltage meters, and the like. I expect most organizations deal with "expendables" like batteries in one of two ways:
1) keep spares handy for instruments which use them and replace as necessary
or
2) deal with them like major office buildings deal with ceiling lamps to save labor costs because the labor cost is more than the cost of the expendable product - replace ALL on a schedule which is shorter time period than useful life of the product (you still have to keep some spares on hand for "lemons" and extraordinary usage, though).

It occurs to me to elaborate on labor cost:
A trip to a tool crib for a $20/hour technician to get a replacement battery is usually more costly than the cost of the battery, so many organizations have tool crib attendant include a fresh spare battery when issuing a battery-operated tool or instrument. In an inspection lab setting, spare batteries ought to be easily accessible and training in use of an instrument should include method of replacing battery.

"Golly, Ken. I guess the rest of us don't think of batteries when we think of calibration. A change of batteries doesn't change calibration of any dimension measuring instrument."

Really...exactly how does one read a digital readout with dead batteries? How many of you change batteries on a regular basis? How many get their instruments from a tool crib attendant who gives fresh batteries when issued? How many have of you have battery replacement as part of your calibration/verification methods?

Maybe you should be thinking about it...

"Golly, Ken. I guess the rest of us don't think of batteries when we think of calibration. A change of batteries doesn't change calibration of any dimension measuring instrument."

Really...exactly how does one read a digital readout with dead batteries? How many of you change batteries on a regular basis? How many get their instruments from a tool crib attendant who gives fresh batteries when issued? How many have of you have battery replacement as part of your calibration/verification methods?

Maybe you should be thinking about it...You read a digital readout without batteries the same way you do when you have your eyes closed.

When you want to read the readout, you open your eyes (or change the battery!)

I have made it a point to issue spare batteries with every battery-powered tool or instrument for past 20 years, including battery-powered screwdrivers and drills for maintenance folk. I sure don't want a $30/hour millwright wasting time getting a new battery for a nut driver when I have a $200/hour machine down that needs 100 bolts reinstalled after repair. Where available, we have rechargeable batteries and chargers. For disposable batteries, we maintain inventory just as we do for ballpoint pens, wipers, eyeglass and lens cleaners, spare lamps for optical comparators, microscopes, flashlights, and PowerPoint projectors, etc. That's pretty much what the MRO function of Purchasing is all about!

For crying out loud - our business is to PREVENT discrepancies, not whine about them!

I agree providing SPARE batteries with equipment is a good idea if it is a LONG trip to the tool crib and the company can't/won't afford to pay the employee 5 minutes to grab a battery.
But unless you company enjoys throwing out $2 (or more) batteries on a daily basis, that seems like a real waste to provide NEW batteries EVERY time a tool is issued.
Talk about potential for COST SAVINGS.
We have electric calipers for the entire shop (less than 20) and about 3 electric mic.
When the battery dies, they grab another gage and give the dead one to me.
If we have any in house I throw one in.
If not time to order.
Actually I have 2 dead batteries in 2 of 3 electric mics that are currently stored.
Guess what, I'm not putting new ones in until some one needs them!

Batteries???

My ruler and tape measure don't have any batteries :vfunny: :p

If previous results indicate that an item has not been found to be out of calibration, is it acceptable to expand the calibration frequency past the manufacturers recommended calibration cycle or should we always follow the recommendation?
:bigwave:

Yes, a recommendation is exactly that - a recommendation. It is not a mandate. Much depends on the frequency of use, the environment, the skill of the user, etc.

We have a vibration analyzer that has an OEM recommended "calibration frequency" of one year. However, we produce about 4 machines per year that require use of the device. Four times between calibration isn't much use, so we extended it to five (5) years.

Once again, compare benefit to risk. If there have been no problems, keep extending.

Absolutley....

...and if they are very rarely used, how about "To be calibrated before use"?

/Claes

Thanks for the feedback guys,

The items that I am mainly concerned with are light loss meters and pin gauge sets. We have reviewed the calibration records from our external calibration sources and determined that the tools in question have not been out of calibration at any time therefore, I am considering extending the calibration frequency from 1 to 2 years and possibly further depending upon future results.

mshell

We have a customer that says we need to set a top end of our interval adjustments. We're using a modified NCSL RP-1 adjustment frequency, with the multipliers adjusted to match our onsite calibration frequency. Has anyone else ever been required to set an upper limit on a quasi-statistically based frequency?

deniser,
We have never had a customer request this.....

Do they know what they are asking or is this some young engineer that does not have a clue? (Sorry, I do not mean to offend anyone)

We have has stipulated government spects but nothing more than that.

Cindy

Cindy,

He's not a new engineer. He's been around a while. It is my opinion that our system will self regulate itself and find the right maximum for the equipment. He is concerned that the interval might stretch beyond 5 years. In some cases it might, but that equipment would also come with a 20 year history of good calibrations without an adjustment needed. If it fails, we halve the interval and hold at that level for at least 3 good cycles before starting to increase the interval again. I believe we'll know when we reach the max for that unit.

If I were your customer, I would actually worry as well, unless you answered a few questions. Long intervals work, especially on extremely stable gauges that receive no abuse. The problem is that with a 5+ year interval, the abuse could happen, and there could be years that the gauge is erroneous.

My questions would be:

Are the gauges checked in-process? (i.e., a quick check every month to give a level of confidence)

Are there records that show that your interval computation is statistically sound?

Is the new extended interval set to recalibrate just BEFORE the gauge goes out of specification, or just AFTER the gauge goes out of specification?

Sorry, I just a needed to play a bit of the devil's advocate on a Friday before I go home. It's been a long week of employee performance reviews, and I needed a technical break to ease my mind.

Ryan

Ryan,

No problem playing devil's advocate. I'm trying to find out if we're really missing something by not setting an upper limit.

The gauges that adjust their intervals are not mechanical or dimensional. Damage to them would be apparent. They're items like pulse generators, power supplies and other electrical output units. The output is often read by another unit. They're all units that we've had 15-20 years. A lot of the users were on the teams that developed these units and they know immediately when the unit has a problem. All are in engineering, not in production.

Our intervals are not exactly in compliance with NCSL's methods since we do not have an in house calibration facility and must rely on subcontractors to come onsite twice yearly, though we've tried to stay as true to the method as we can.

There is a practical limit to the cal interval. People tend to get nervous at the 4-5 year cycle and decide the risk isn't worth the potential cost savings and take the units off auto-adjust. Our longest interval is currently 5 years, and those units have been in the closet for 2 of those 5 years.

We just had our onsite. They did 196 units. 2 failed. One was ESD zapped by the calibrator. The other was broken and needed a new jumper. Nothing needed adjusting. I can't recall a time where we've had more than 1% OOT's.

I suppose we could do something extremely silly like put an upper limit of 20 years, but I'd rather not set a limit unless it has meaning.

deniser,

Can't say as I blame you. We have a lot of calibration certificates for equipment that has never been out of calibration plus we perform pre/post test through the whole chain for any test. We are certain that all equipment used is functioning properly and we have the pre/post verifications. We try to lower our required calibrations as well due to the cost of some of the calibrations. But honestly, anything over 5 years is cause for concern.

Can you prove that the equipment is verified and can you provide evidence?

And on another note, if the customer is requesting this to ensure correctness and the customer is knowledgeable, I probably would do the calibration just to give the customer that warm fuzzy feeling and keep them happy. Maybe in time with support of data the customer can see your point.

Cindy

Wow! This is a great thread!

For the general use of folks with lots of gages that are primarily micrometers, calipers, dial gages and so forth......look at your actual use and environment. If the use is daily, and it is a machine shop or test lab environment then more frequent calibration than annual might be appropriate. If in a well-controlled environment, rarely used, stored carefully, then a longer cycle is certainly appropriate (with a few exceptions).

Beginning with annual is the typical starting point. Adjust from there based on calibration history and preferably by using NCSLI RP-1 as a guide. Your accredited third party calibration provider should be able to advise you, based on history of the item, and the use and environment it is in. That of course will depend somewhat on the calibration provider having the history of the item.

Also, remember that in some cases, changing a battery/fuse is considered a repair and therefore gets a repair charge from the calibration provider. This is the case when batteries and/or fuses are built in to the unit such that the same opening must be made to adjust or change a battery/fuse. Generally, this is electronic items, not calipers. Ask your calibration provider about that before having them change the battery/fuse, and ask how much the repair charge is. I have seen as high as $120 per hour for repair, and changing a battery can take as much as 15-20 minutes depending on unit. For fuses, a solder-in fuse is actually a repair, but a snap-in fuse is a consummable.

Hope I haven't scared too many folks......

Hershal

We have a customer that says we need to set a top end of our interval adjustments. We're using a modified NCSL RP-1 adjustment frequency, with the multipliers adjusted to match our onsite calibration frequency. Has anyone else ever been required to set an upper limit on a quasi-statistically based frequency?
The cal lab I am working with is the in-house electronic calibration facility for a major airline. We have decided on these rules and written them into the appropriate quality policy:

Calibration interval analyses are based on methods in NSCL RP-1 (usually method A3) at 95% end-of-period reliablity and 95% confidence level. Interval adjustments are done on a model number basis where possible -- all Fluke 87 meters, for example
If the data supports an increase in the interval, we limit the maximum increase to 50% of the current interval. (for example, if a meter is currently calibrated every 12 months it would be extended to no more than 18 even if the data supports more than that.)
The maximum calibration interval allowed is 60 months (5 years).
The limits on amount of increase and on maximum interval are deliberately conservative because this industry is intensely safety-conscious. Making a major change like doubling or tripling the current interval is much too far outside our comfort zone.

A few general obervations:
It takes much less data to reduce an interval than to increase one. For example, an item had 2 repeated OOT events at a 3 month interval so it was reduced to 1 month. There is very little likelihood that it would pass the next 40 consecutive calibrations - which is what would be required to maintain the 95% reliability. (That model is also going to be replaced.)

Recognize that where there are fewer than 10 units of a model number in the company, it is unlikely for them to ever have their interval increased by using any of the easily-implemented methods in RP-1. This is because the time required to gather data for a statistically valid analysis exceeds the probable useful lifetime of the equipment.

In about 20 years in several different industries I have never seen an interval longer than 72 months -- and that was for totally passive items like waveguide directional couplers.

Yes, a recommendation is exactly that - a recommendation. It is not a mandate.
Except ... if you are in a regulated industry (medical, nuclear, aircraft maintenance, etc.) then the regulatory agency probably has a few things to say about it.

The FAA, for example, requires first recording actual data (not pass/fail) for every calibration; and statistical analysis of the data history to determine the interval. If you are referring to NCSL RP-1 for methods, the statistical requirement means that you cannot use methods A1 or A2 -- which happen to be the two most widely used methods.

Wes,
You are correct....and for as long as I have been in the quality field..the term "calibrate" has actually meant "to check". Calibration is the adjustment you make for an out of tolerance condition. But to make things as easy as possible in the worlds we work in...I think we all refer to the function as "Calibration".
Right or wrong....IMHO it is just semantics. As long as the message is understood.

CarolX
Short definition: calibration is verification of the instrument's performance with respect to its performance specifications, by using external calibrated and traceable measurement standards of known value and uncertainty.

Long form of the definition: First, all of the above. Then, if indicated by the results of the initial calibration run, adjustment or repair to restore proper operation. Finally, another calibration run to verify that the performance meets specifications.

The basic premise of a proper calibration procedure is that the instrument is in good working order and only needs to have its performance verified (NCSL RP-4). The calibration is performed with the instrument in its normal operating configuration.

The problem with the "calibration" procedures in most manufacturer's manuals it that they start by assuming that the instrument always needs adjustment. In general, adjustment is only required if the calibration (performance verification) either fails or a result is in the area of a specification limit +/- the uncertainty of the measurement standard. Adjustment may be performed in other cases where the result is within specification, but with cautious awareness of the risks of tampering with a process.

I was scanning the board for an answer to a similar question...we have a Fowler Optical Comparator Set which might be used once a year, maybe twice. I was told by an engineer at the OEM that the shift over time in accuracy is negligible. Basically, what I am looking for is substantiation for extending the interval out as far as feasibly possible. If I can justify it on paper, management, auditors, and integrity will be satisfied.

Any help will be greatly appreciated!

I was scanning the board for an answer to a similar question...we have a Fowler Optical Comparator Set which might be used once a year, maybe twice. I was told by an engineer at the OEM that the shift over time in accuracy is negligible. Basically, what I am looking for is substantiation for extending the interval out as far as feasibly possible. If I can justify it on paper, management, auditors, and integrity will be satisfied.

Any help will be greatly appreciated!

Use the history of the comparator to justify the calibration interval. If the device is always within tolerance when received for calibration, extend the calibration interval. You can also keep track of the no. of times used and set an interval based on that. You might also want the OEM to put in writing the accuracy shift over time.

I was scanning the board for an answer to a similar question...we have a Fowler Optical Comparator Set which might be used once a year, maybe twice. I was told by an engineer at the OEM that the shift over time in accuracy is negligible. Basically, what I am looking for is substantiation for extending the interval out as far as feasibly possible. If I can justify it on paper, management, auditors, and integrity will be satisfied.

Any help will be greatly appreciated!Good question, blemon! Welcome to the Cove:bigwave:
Al Rosen has good advice here.

Typically, an OEM will have suggested intervals for calibration and recertification of instruments and gages based on amount of usage over time. A big company like Fowler should have this available as a simple handout (it may have even been included with the set when purchased.)

If the manufacturer or its engineering staff is unavailable or reluctant, you can arbitrarily extend the time between calibration/certification events to any number of days, weeks, etc., maintaining a protocol or instruction to check its reading against a known standard for calibration purposes before measuring a workpiece. (This is also a way of helping reorient the technician to an unfamiliar instrument and helps take the human error out of a measurement.)

I am fascinated by all of the good positive comments on calibration frequency and over the years (Mil-Q, Mil-I and Mil-C environments) have used most of the rules for extending calibration intervals. Let me add just three notes:
1) Make sure your calibration procedure spells out the rules for extending intervals and who will make the decision to extend.(Usually QA Manager)
2) In the past I have had great success using seals. (I have used wire with lead seals, plastic seals, wax seal and tape seals). These seals work quite nicely on crimping tools and electronic test equipment. If the seal is unbroken at time of recalibration then the tool/instrument has not been used and may be extended.
3) Finally, if the "test sets" inputs and outputs are independently verified by calibrated meters such as Fluke, etc. then there is no need to calibrate the "test set". Only the instrument verifying final acceptance needed to be calibrated. The "test sets" were marked "no calibration required". These test sets were used to verify the performance of printed circuit boards and wire harnesses.

I might add that many of the test were witnessed by customers and government reps and they preferred the independent verification methods.
:2cents:
Jim Howe

is it true equipment for temperature, pressure and electrical must be calibrate once a year? can it be longer/extend?

Is it not possible to just get an onsite service from you calibration provider and get those items verified/calibrated at your location? This would reduce down time to a matter of 15-20 mins (per dial indicator) on the item instead of 5 working days, esentially eliminating the need for redundent items for down time.

Depending on your location, the money you could save from not getting the others calibrated might cover the onsite fee the provider would charge.

Get your back ups calibrated and sealed up in a bag, keep them purely as backups incase something breaks.

Just a thought,
Mark.

One tool that is often ignored in determination of calibration frequency is stability. For dimensional gages, it would make sense that your calibration data over time should show the rate of wear. That is one reason why your calibration standards should be at 10:1, to have enough resolution to detect such changes. You may consider using that wear rate from a linear regression of your calibration data, and extrapolate it to the endpoint of your gage tolerance. If you are making adjustments, you will have to track the before and after dimension, and add the change to original dimension to chart the actual wear. Divide that time by 3 or 5 (whatever you feel comfortable based on your usage so as to not overshoot the limit) to determine a sane, justifiable calibration frequency. Not the best explanation - but, in essence, handle the issue that same as tracking tool wear. (Yes, that means do not X-bar R the stability measurement, it should be non-normal. You might have figured that was coming...:cool:)

It is a judgment call, that you should make based on the severity of your measurements. Depending on the gage software you use, you may be able to generate a graph to show the results of wear, and you should be able to use this info to help you make an informed decision. I use GAGEtrak v.6.5 and it has a graph feature that I use quite frequently.

One factor that does not come out of tracking wear is the risk of a 'special cause' such as dropping a gage. If one decided to make the calibration period 2 years, but the gage is dropped in 30 days, you have 1 year and 11 months of suspect product. It has been known to happen with dire consequences. That said, the point is the decisions need to be made with "profound knowledge" of the entire system - how it is used, risk of damage, wear rate, etc. There are a lot of folks looking for the magic bullet of when to calibrate (and how to calibrate as little as possible). Usually, the bullet they get is in their foot... :cool: