Steel Tape Rules - Does the length of the leads have a significant impact?



An important question is "does the length of the leads have a significant impact on the quality of the measurement?" The answer is probably "No" unless you are working with UHF or microwave radio frequencies, or with very high current or very low resistance. The length requirement most likely comes from the fact that it is a common stock length, is convenient to work with, and is probably what the original engineer happened to have on hand.

If the length truly is not critical, is it possible to change the implied exact measurement requirement to something with more flexibility? Then you can get back to the work of generating income by repairing widgets.

If the length truly IS critical, there should be a tolerance listed, and in that case the cable needs to be measured and marked with the length. If this is the case then you MAY need a calibrated rule if it is your usual practice to make these cables as needed. And you have to have a procedure for making cables. (and lots more ...) Or if you normally purchase cables, then you have to start inspecting them for that parameter. (As you can see, a small question can generate a lot more "stuff".)

So first, ask how important the "three foot" value is, and document the answer.

(Another question is "does this requirement come from a bureaucratic organization that requires 100% verbatim compliance?" In that case, the easiest solution often is to quietly surrender and do what they say.)

Graeme C. Payne
ASQ Certified Quality Engineer

[This message has been edited by Graeme (edited 21 November 2000).]

Alf Gulford

As they're used here, steel rules, tape measures and yardsticks don't need to be calibrated and that's what we say in our M&TE procedure. We do say that before use the assember must visually check for damage (e.g.; tape measure end bent in or out). This has been acceptable to two registrars.



If you have already specified a method for checking the tapes before use (the visual you described) then to make sure that it is clear the status of the tapes, I would add a "working Equipment" or "Reference Only" or "Not in Calibration System" or even a "Verify Before Use" label on each tape/device.


Steel Tape Rules

We are being audited very soon. Today I was informed that I had to have a calibrated steel rule for my division and that anyone who had a steel rule in their tool box had to have a reference only sticker put on it. We are a repair shop and the CAR that resulted in this new rule stated: "The special instructions on a repair asked for three foot testleads. The technician used his own tape measure to cut the wire for these leads. This tape was not calibrated." Is it that critical?!

Steven Truchon

For what its worth, in my life I have owned a steel rule and a tape measure that were both at about 7/8 scale. One inch on the steel rule measured .875

Over 3 feet, that would yield a 4.5 inch error! Prior to that I scoffed at anyone requiring "calibration" of such tools. But I quickly found that a simple documented verification was worth the little time it took to have it done.


In our facility we use many steel tapes and rulers to verify cutting lengths of cable and small diameter tubing. We have determined that the length of these cuts are important to the quality of the finished product and tolerances have been assigned. As we receive any steel tapes and rulers, we verify their measurements against our standard. About 5% of them have been rejected, usually because of a faulty starting edge. Those that pass the initial verification are then checked on a regular basis for damage that would affect accuracy or readability. This is a documented procedure that has stood through all of our audits.


I recently talked to a person who is an "Inspector" for a well know measuring tape manufacturer. I laughed and asked what do you inspect? He commenced to relate some horror stories of contractors using defective tape measures that were 1" short in 25 ft. There was actually 1" missing on the metal roll. The fact that an individual can make a living inspecting measuring tapes tells you that they are not perfect.

David Drue Stauffer

Hi guys, I would like to throw in my two cents. Calibration of measuring instruments is required on any items used for the purpose of product acceptance. If a gage is used to measure characteristics that appear on a drawing that has specification limits associated with it, that gage or gage system (surface plate, height gage, & test indicator in combination) is subject to regular calibration. End result is that your product acceptance is based upon the measurement results produced by that measurement system.
Also, good metrology practice states that anytime you are relying upon a tape measure or scales, measurements should me acquired by starting at the 1" line and taking the measurement from there rather that relying upon the measurement from the end which is highly susceptible to damage causing measurement error. Also, any linear measurement device should be verified for accuracy against a standard of known values before it is put into service. This may be as simple as the comparison to two other linear measuring devices that are in agreement with one another if a standard is not available.


Hi folks,I`ve been charged with the calibration duties at our ISO 9001 certified yacht building facility. Our registrar suggested at our last surveillence audit that we need to calibrate all of our tape measures in-house. Tape measures are used in all areas of our business, we`ve got a pile of them. Do any of your companies supply tape measures? How do you police the many tapes out there on the manufacturing floor? Also, must a certified master be used or can we simply designate a new steel yardstick as our master and go from there?
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