Calibrating or Verifying Metal or Steel Tape Measures

dwperron

Trusted Information Resource
I have seen a process where the tape measures are calibrated using another tape measure. All tape measures were of the same brand and length. One tape measure was kept as a "master" and sent out annually to an accredited lab. All other tape measures would be compared to this tape measure. Is this an acceptable method to calibrate tape measures? The part that I found questionable is that the master tape measure listed its tolerance as +/- 1/32". The tape measures calibrated using this master tape measure were also stated to be at +/- 1/32"
This depends on your definition of "acceptable".
You can compare a tape measure to a "master", it is done. In this case you would be accepting a measurement uncertainty that is larger than the tolerance of your tape measure, so that will determine if the calibration is "acceptable" to your requirements.
I have attached a NIST SOP that uses this method to calibrate a tape measure.
 

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What if the Tape was not put to use say for 3 months after being bought along with Calibration certificate.Now when it should be calibrated? Is it one year from the Start date of Actual Usage or one year from the date of Calibration as mentioned in the certificate. Assume the tape was preserved well while in Storage. I have this issue in my organisation. how to answer the auditor reg this.thank u
 

Helmut Jilling

Auditor / Consultant
What if the Tape was not put to use say for 3 months after being bought along with Calibration certificate.Now when it should be calibrated? Is it one year from the Start date of Actual Usage or one year from the date of Calibration as mentioned in the certificate. Assume the tape was preserved well while in Storage. I have this issue in my organisation. how to answer the auditor reg this.thank u
There is a very easy way to verify if a measuring tape is accurate - calibrate a 3 or 6 ft quality steel rule and verify your tape measures to the calibrated steel rule. There is measurement certainty with the steel rule.... if the tapes match the increments, then the tape is accurate as well. I have seen tape measures which were off by 1/8".... it can be a problem....
 

Jen Kirley

Quality and Auditing Expert
Staff member
Admin
In addition to the consequence of wear and tear (the rivets holding the hook wear and elongate the holes, adding as much as 1/16 inch to the total length) I once purchased a tape measure that I was amazed to find significantly off: I mean almost 1/8 inch short in every 12 inches. It was a cheap model, I never see that in the name brand tape measures. I have often wished I'd kept that "black sheep" tape measure; it would make a good case study.
 

Jen Kirley

Quality and Auditing Expert
Staff member
Admin
What if the Tape was not put to use say for 3 months after being bought along with Calibration certificate.Now when it should be calibrated? Is it one year from the Start date of Actual Usage or one year from the date of Calibration as mentioned in the certificate. Assume the tape was preserved well while in Storage. I have this issue in my organisation. how to answer the auditor reg this.thank u
Setting up verification plans for measuring instruments is pretty consistent in the general rules:
  • Wear and tear in typical use (environment and handling by users)
  • Protection when not in use
  • The instrument's sensitivity or ruggedness
  • Amount of use that incurs wear in even best case scenarios
  • The tolerances you are expected to meet
  • The cost of getting it wrong
Tape measures are among the most underappreciated of measurement instruments. It would be easy to question the expense of purchasing a tape measure that comes with a calibration certificate, but as I described above, I once purchased a (cheap) tape measure that was significantly short. I mean almost 1/8 inch short in 0-12 inches, another (almost) 1/8 in 12-24 inches, etc. For a lot of applications, real accuracy seems unimportant but I once had a client that fabricated 10-foot-square catalytic converter units for coal and gas-fired power plants. If size and squareness was off by much, these products might not fit or their effectiveness could be impaired by escaped gases. We can't have that... so yes, it can sometimes really matter.
 

Jim Wynne

Staff member
Admin
The only reasonable answer as to whether a tape measure needs to be calibrated is, "It depends." It's all about risk and choosing the right device for the task. If an error of 1/8" (.125) in ten feet can cause a significant problem, a tape measure isn't the right device.

EDIT: See this post from 11 years ago.
 
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