In part, the answer to this question depends on the tolerances used in the manufacturing process. As you look at the end tab on a typical tape measure, you notice that it slides to accommodate both inner and outer measurements. The amount of adjustment is supposed to be the thickness of the end tab – typically 1/32″. If the end tab movement is greater than that amount, then you have a potentially inaccurate tape measure. If you are working to tolerances larger than 1\32″, for example, +/- 1/8” then you do not need to calibrate the tape, as there is no potential for adjustment – the scale on the tape is pre-printed, with no other adjustment possible. You do need to inspect the tape regularly, say at 6 month intervals, to ensure that the scale is still legible, and that the end tab play is still correct.

If you work to tighter tolerances, or are concerned with this approach, you have an alternative. Purchase a brand new Lufkin or Stanley Tape measure. A trip to their website will show that all tapes are produced in accordance with their ISO 9001 program, and are verified as accurate to international standards. Keep the new “calibrated and traceable” tape for checking the other working tapes, then conduct those checks twice yearly.

A copy of the text from the Lufkin site is included for your information.

LUFKIN TAPE CERTIFICATION AND ISO

Many end-users are registering for ISO certification. If they use measuring tapes as part of their production processes, it is advisable to establish procedures requiring the use of a certified tape as a master. Lufkin® provides selected certified tapes in excess of 50’ for standard charges (which include the purchase price of the tape). Short tapes are not calibrated, but are checked for accuracy. Lufkin’s test procedures are traceable to the National Institute of Standards and Technology.

– Ted Uffen, BRC Quality Consultant