The lesson will cover specifications, tolerances, accuracy, and uncertainty ratios, and guardbanding. On completion, you will understand these topics and will be able to understand how to read and interpret published specifications, and how to calculate accuracy ratios and guardbands for 17025 compliance.

Scope of the Lesson

Outline

Introduction
   • Communicating about measurements and measurement equipment

What is a Specification?
   • Why do we need specifications?
   • The use of specifications in measurement and metrology
   • The form(s) taken by specification
   • Some examples of specifications of measuring equipment
   • How to read and interpret specifications
   • The importance of specifications in calibration
   • What it means to be in or out of spec.
   • Practice reading, interpreting, calculating

What is a Tolerance?
   • How are tolerances stated?
   • What is the difference between a tolerance and a specification?
   • Some examples of tolerances of measuring equipment
   • How to read and interpret tolerances
   • The importance of tolerances in calibration
   • What it means to be in or out of tolerance
   • Practice reading, interpreting, calculating

Measurement Uncertainty (this is not a full treatment, just an intro in context)
   • Definitions (in context) of measures of measurement reliability and quality
   • Accuracy
   • Precision
   • Resolution
   • Repeatability and Reproducibility
   • Traceability
   • How do these definitions fit with specifications and tolerances?
   • Special cases: floor specs, % of full scale vs % of reading, ppm, values near zero
   • Calculation of measurement uncertainty – budgets
   • Converting specifications and tolerances to uncertainty
   • Practice calculating

Accreditation: rules relating to specifications and tolerances

Ratios
   • The 10:1 principle; 4:1, 3:1
   • What did they mean in the past: Definitions in MIL-STD-45662
   • What do they mean now? Definitions in ANSI/NCSL Z-540-1, ISO 10012-1
      and ISO/IEC 17025
   • Are they useful? If so, why?
   • Accuracy ratios, tolerance ratios, uncertainty ratios
   • Ratios and traceability
   • Practice calculations

Specifications, Tolerances, and Uncertainty
   • Inspection and test
   • Errors of Type I
   • Errors of Type II
   • Decision rules
   • Definitions
   • Applying them
   • Responsibility (whose)
   • Measurement uncertainty and decision rules

Changes to and Adjustment of Decision Rules
   • Guardbanding
   • Determining conformance to identified metrological specifications and
      taking measurement uncertainty into account
   • Practice calculations

Evaluation and Exam