Calibrating or Verifying Metal or Steel Tape Measures

metaltesting54 said:

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"

Click to expand...

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.

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

visvan1970 said:

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

Click to expand...

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....

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.

visvan1970 said:

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

Click to expand...

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.

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.

Hahaha... My technician tells me to scrape calibrating tape measures. Reason? He lost one of the tape measures AND argues that the tape measures are only use at the production floor only. Seems like I can't and I got a whole lot of comments here to back me up.

In some instances it is cheaper to buy a new tape measure with a cert than it is to calibrate. Usually when you think of a tape measure, it is not something one would use to make precision measurements.

"Usually when you think of a tape measure, it is not something one would use to make precision measurements. "
Key word - "usually".

Maybe so, but when I worked in a modular home factory, "small" discrepancies like 1/8" could easily be catastrophic, as each "module" could be out that much end to end, and they all had to match up within 1/8" as a total unit. There could be up to 8 "units" in each house.
I remember calibrating tape measures a steel (invar) tape that was calibrated by NIST. This was an easy check in house to verify the production floor tapes.

There are no requirements that the steel tape needs to calibrate in the standards documents or other specifications and the facility can build up corresponding control requirements according to actual conditions. That whether the steel tape needs to calibrate is depends on your own decision about it.