International Standard Iso 14253 1.pdf -
Imagine a shaft diameter with (\textLSL = 10.00\ \textmm), (\textUSL = 10.10\ \textmm), (U = 0.02\ \textmm).
Thus the specification limits are 10.00–10.10, but the acceptance limits for proving conformance are 10.02–10.08.
ISO 14253-1 creates three distinct zones based on the measurement result ($y$) and the expanded measurement uncertainty ($U$). The limits of specification are defined as the Upper Specification Limit ($USL$) and Lower Specification Limit ($LSL$). INTERNATIONAL STANDARD ISO 14253 1.pdf
The most interesting aspect of this standard is how it fundamentally changes how we view a simple "Pass/Fail" result.
In a traditional engineering class, you might measure a part, get a number, and compare it to the drawing. If the drawing says $50 \pm 1$, and you measure $50.5$, you might say "It passes." Imagine a shaft diameter with (\textLSL = 10
ISO 14253-1 argues that this is wrong because no measurement is perfect. Every measurement has an uncertainty interval (usually expanded uncertainty, $U$).
The text is interesting because it transforms measurement from a passive observation ("The number is 5.0") into a probabilistic legal argument ("I have proven with 95% confidence that the number is within limits"). It forces engineers to acknowledge that nothing is exact and provides a strict mathematical framework for handling that ambiguity. Thus the specification limits are 10
Are you looking for clarification on a specific section of the text, or perhaps trying to apply these rules to a specific measurement scenario?
Only one side of the specification limit is active. The rule applies symmetrically on that side.