Documented information of fitness in 7.1.5.1

There are now so many ways to show calibration and verification, it seems an obscure-sounding blanket statement helps. The term to keep in mind here is "appropriate."

I have participated in many discussions regarding terminology (calibration versus verification) and the 1/10 principle, which I have heard so many times through the years that I talked about it as a "rule of 10 to 1" until an associate invited me to tell him where I got this rule. I researched exhaustively and found no mention of it. Since then, someone told me they though it came from an old British standard. I have seen 4-to-1 used too, but 10-to-1 is simpler and, in my view more risk averse.

Certificates almost never include mention of this detail. Certificates for scales do often refer to NIST Handbook 44, but seldom to Section 6 Table 6 (watch out, Handbook 44 has been revised) where tolerance is established based on criticality. It would be good to determine the Class if you are working with scales calibration, and ask your service provider to indicate pass/fail based on that acceptable error. If providers only give numbers but no Pass/Fail, it could well mean they have never been informed of the Class or required tolerance. This is where fitness for purpose comes in, also in listing the instrument's (any instrument, not just a scale) physical condition at time of calibration/verification.

So ideally, whatever form of documentation you retain, I would hope to see at least:

• Identification of the instrument
• Date of calibration/verification check
• Pass/Fail determination of accuracy
  
• Intervals of the check
  
• Amount of error in numerical terms for each interval
• Physical condition at time of check
  
• Test method or procedure used
  
• The traceable standard(s) used to do the calibration/verification. If no traceable standards are available, list what was used.
  
• Name of the technician performing the check
• Next due date

I think that's it.

I usually see a schedule of some kind, listing what is coming due when. My clients usually understand that frequency of the calibration depends on the instrument's sensitivity, the tolerances, the instrument's storage, typical use and handling, and the cost of getting it wrong. Very often there will be 2 sets of gage blocks. One is used daily and gets checked annually, while the other is kept put away for use within the lab and when the shop set is out for check. Because of its usage, it gets a 3-year frequency.

Sometimes my clients will adjust their schedule based on the tool's performance. Being able to demonstrate that (could be charts or notes) is excellent to support the fitness for use principle.

I hope this helps!

 

I'm struggling to understand this statement, and reconciling it with time-based calibrations, like once a year or every three years. Help!

 

The time is set based on factors that may add risk of the instrument's not performing reliably.