The manufacturer's stated performance limits for an instrument, usually written as ±(percent of reading + percent of range) or ±(ppm + counts), and tied to a time since calibration and a temperature band, such as 24 hours, 90 days or 1 year at 23 ± 5 °C. Labs use a spec as a Type B input, treated as a rectangular limit, when they rely on a standard's published performance rather than its individual certificate history.
We're relying on the 90-day spec for the calibrator, so it has to stay inside 90 days of its last cal.
Read the footnotes: a spec quoted at Tcal ± 1 °C balloons once the meter sits on a bench at 28 °C.
Also heard as
- specs
- accuracy spec
- one-year spec
Related terms
Accuracy
How close a measured value comes to the true value, a qualitative idea rather than a reported number.
Counts
The steps of the last digit on a digital display, used in specs such as plus or minus 2 counts.
Type B evaluation
Sizing an uncertainty component from existing knowledge such as certificates, specs or resolution, with no new repeat data.
Rectangular distribution
A distribution giving equal likelihood to every value between two limits, used when only the bounds are known.
Tolerance
The allowed deviation from nominal that an item or instrument may show and still be accepted.