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Measurement tools and calibration · Lesson 2 of 4

Measurement tools and calibration: materials, standards and design constraints

Tape accuracy in NIST Handbook 44 and OIML R 35-1, the 20 °C reference temperature and heat on a 10 ft piece, why a gauge number is not a thickness, traceability and certificates, calibration intervals, and the resolution AFS hems ask for.

You will be able to: State what limits a reading: the accuracy benchmarks for tapes, the 20 °C reference temperature, the effect of heat and of gauge systems on a thickness, the traceability chain and calibration certificates, and the step size AFS sizes demand.

15 min · 12 slides · 11 questions

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Slide 1 of 12

Handbook 44: tape tolerances by length

NIST Handbook 44, section 5.52, covers any linear measure. Its Table 2 gives the tolerance for metal tapes, in excess and in deficiency, by length from zero.

For a length of up to 6 ft from zero, the tolerance is 1/32 in.

From 7 to 30 ft from zero it is 1/16 in.

From 31 to 55 ft it is 1/8 in.

From 56 to 80 ft it is 3/16 in.

From 81 to 100 ft it is 1/4 in.

Allowed error of a metal tape by lengthBar chart of the NIST Handbook 44 tolerance for metal tapes: 1/32 in up to 6 ft, 1/16 in from 7 to 30 ft, 1/8 in from 31 to 55 ft, 3/16 in from 56 to 80 ft and 1/4 in from 81 to 100 ft. The 7 to 30 ft bar, which covers a 10 ft tape, is highlighted.Allowed error of a metal tape10 ft1/16 in1/8 in3/16 in1/4 in1/32 inup to6 ft1/16 in7 to30 ft1/8 in31 to55 ft3/16 in56 to80 ft1/4 in81 to100 ftAllowed error (in)Length measured from zeroNIST Handbook 44 (2026), 5.52, Table 2

Bar chart of the NIST Handbook 44 tolerance for metal tapes: 1/32 in up to 6 ft, 1/16 in from 7 to 30 ft, 1/8 in from 31 to 55 ft, 3/16 in from 56 to 80 ft and 1/4 in from 81 to 100 ft. The bar for 7 to 30 ft, which covers a 10 ft length, is highlighted. The axis is the length measured from zero.

NIST Handbook 44 (2026) section 5.52, Table 2. The longer the tape, the more error is allowed; it is a benchmark, not an AFS or order tolerance.

Sources

Glossary

Metrological traceability
A property of a result: it can be related to a reference through a documented unbroken chain of calibrations, each contributing to the measurement uncertainty (NIST). Traceability alone does not guarantee a tool is fit for a job.
Expanded uncertainty
The doubt stated with a calibrated value, written y ± U, reported with its coverage factor and coverage probability on an accredited calibration certificate (NIST Handbook 150-2).
Accuracy class
A grade given to a material measure of length, such as OIML R 35-1 class I, II or III; each class has its own formula for the maximum permitted error.
Reference temperature
The temperature at which a dimension is defined to be correct: 20 °C (68 °F) for dimensional measurement (NIST).
Calibration interval
The time between calibrations of a tool. NIST GMP 11 says intervals start from an initial value and may be lengthened or shortened by documented analysis.
Fixed sheet gauge
A hardened fixed gauge made for one named gauge system, such as Starrett's 283 U.S. Standard Gage for uncoated sheet and plate iron and steel. It gives a gauge number, not a measured decimal (Starrett).