The 10% rule says that if a component tolerance is given as x then the instrument used to demonstrate compliance should have an uncertainty of better than x/10. In practice it is sometimes difficult to get better than 20% (x/5). Whatever the tolerance and uncertainty may be, appropriate decision making rules should be in place. Appendix J of UKAS document M3003 covers statements of compliance with a specification.

The relevant International Standard is Geometrical Product Specification (GPS) - ISO 14253: Inspection by measurement of workpieces and measuring equipment : Part 1 : Decision rules for proving conformance or non-conformance with specifications.