Calibracion De Cronometros

Stopwatch and Timer Calibrations

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

960-12
Special Publication 960-12

NIST Recommended Practice Guide
Special Publication 960-12

Stopwatch and Timer Calibrations

Jeff C. Gust
Quametec Corporation

Robert M. Graham
Sandia National Laboratories

Michael A. Lombardi
National Institute of Standards and Technology

PhysicsLaboratory May 2004
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U.S. Department of Commerce Donald L. Evans, Secretary Technology Administration Phillip J. Bond, Under Secretary for Technology National Institute of Standards and Technology Arden L. Bement, Jr., Director

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◆ Stopwatch and Timer Calibrations

Certain commercial entities,equipment, or materials may be identified in this document in order to describe an experimental procedure or concept adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the entities, materials, or equipment are necessarily the best available for the purpose.

National Institute ofStandards and Technology Special Publication 960-12 Natl. Inst. Stand. Technol. Spec. Publ. 960-12 57 pages (May 2004) CODEN: NSPUE2 U.S. GOVERNMENT PRINTING OFFICE WASHINGTON: 2004 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 ii

Foreword ◆
FOREWORDStopwatch and timer calibrations are perhaps the most common calibrations 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, until now, no definitive text has 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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Acknowledgments ◆
ACKNOWLEDGMENTS
The authors thank the following individuals for their extremely useful suggestions regarding this manuscript: Georgia Harris and David Smith of NIST, Ross Andersen of the New York Bureau of Weights and Measures, Jim Jenkins of Quametec Corporation, andWarren Lewis and Dick Pettit of Sandia National Laboratories.*

* Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin
Company, for the United States Department of Energy’s National Nuclear Security Administration under Contract DE-AC04-94AL85000.

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Table of Contents ◆
TABLE OF CONTENTS
List of Figures..................................................................................... ix List of Tables ........................................................................................x 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 and Coordinated Universal Time (UTC) ................................................................... 5 2. Description of Timing Devices that Require Calibration ..............................................................9 2.A. Stopwatches ................................................................9 2.A.1. Basic Theory of Operation ............................ 11 2.B. Timers...