Cronometros Nist

practice guide

recommended NIST

Stopwatch and Timer Calibrations (2009 edition)

Jeff C. Gust Robert M. Graham Michael A. Lombardi

960-12
Special Publication 960-12
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NIST Recommended Practice Guide
NIST Special Publication 960-12

Stopwatch and Timer Calibrations
(2009 edition)
Jeff C. Gust

Richard J. Bagan, Inc.

Robert M. Graham

Sandia National LaboratoriesMichael A. Lombardi

National Institute of Standards and Technology

January 2009

U.S. Department of Commerce Carlos M. Gutierrez, Secretary National Institute of Standards and Technology Patrick D. Gallagher, Deputy Director

Certain equipment, instruments or materials are identified in this paper in order to adequately specify the experimental details. Such identification does not implyrecommendation by the National Institute of Standards and Technology nor does it imply the materials are necessarily the best available for the purpose. Official contribution of the National Institute of Standards and Technology; not subject to copyright in the United States. _______________________________________ National Institute of Standards and Technology Special Publication 960-12 Natl.Inst. Stand. Technol. Spec. Publ. 960-12 80 pages (January 2009) CODEN: NSPUE2 U.S. GOVERNMENT PRINTING OFFICE WASHINGTON: 2009 For sale by the Superintendent of Documents U.S. Government Printing Office Internet: bookstore.gpo.gov Phone: (202) 512-1800 Fax: (202) 512-2250 Mail: Stop SSOP, Washington, DC 20402-0001

Foreword v
FOREWORD
Stopwatch and timer calibrations are perhaps the most commoncalibrations performed in the field of time and frequency metrology. Hundreds of United States laboratories calibrate many thousands of timing devices annually to meet legal and organizational metrology requirements. However, prior to the publication of the first edition of this guide in May 2004, no definitive text had existed on the subject. This NIST Recommended Practice Guide was created to afill a gap in the metrology literature. It assists the working metrologist or calibration technician by describing the types of stopwatches and timers that require calibration, the specifications and tolerances of these devices, the methods used to calibrate them, and the estimated measurement uncertainties for each calibration method. It also discusses the process of establishing measurementtraceability back to national and international standards.

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Acknowledgements v
ACKNOWLEDGEMENTS
The authors thank the following individuals for their extremely useful suggestions regarding this new revision of the guide: Georgia Harris and Val Miller of the NIST Weights and Measures Division, Warren Lewis and Dick Pettit of Sandia National Laboratories, and Dilip Shah, the chair of theAmerican Society for Quality (ASQ) Measurement Quality Division.

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Table of Contents v
Contents
Section 1: Introduction to Stopwatch and Timer Calibrations ............................ 1 1.A. The Units of Time Interval and Frequency ................................... 1 1.B. A Brief Overview of Calibrations ................................................. 3 1.C. Traceability andCoordinated Universal Time (UTC) ................... 5 Section 2: Description of Timing Devices that Require Calibration .................. 9 2.A. Stopwatches .................................................................................. 9 2.B. Timers .......................................................................................... 13 2.C. Commercial TimingDevices....................................................... 14 Section 3: Specifications and Tolerances .......................................................... 15 3.A. Interpreting Manufacturer’s Specifications.................................. 15 3.B. Tolerances Required for Legal Metrology ................................... 19 Section 4: Introduction to Calibration Methods...................................................