NIST UPDATE - Physics Laboratory Articles
February 21, 1995

NIST Physics Data Now at Your Fingertips

NIST's Physics Laboratory is now providing researchers around the world with instant access to data through the Internet. The NIST Physics home page provides links to critically evaluated data as well as general information on research and activities. Computer users can access databases that provide atomic and molecular wavelength and intensity information in both tabular and graphic form. Another electronic database provides energy level and transition probability data for a number of elements. Recommended values of the fundamental physical constants also are provided. Users can log in, search by a menu-driven set of commands, and save and retrieve files of data. Also available are extensive bibliographies on atomic transition probabilities and line shape parameters, listings of references to articles on critically evaluated spectroscopic data, descriptions of programs and facilities in the Physics Laboratory, and published Physics Laboratory articles of wide interest. Researchers with Internet-access and World Wide Web browser software, such as Mosaic or Netscape, can link to the NIST Physics Laboratory home page ( or go directly to the Physical Reference Data page (

Media Contact: Linda Joy,
Phone:(301) 975-NIST (6478)

Enhanced Frequency Calibrations Offered

NIST's Frequency Measurement and Analysis Service has been upgraded significantly in resolution, accuracy and capabilities. It now offers better than 40-picosecond single-shot resolution (1,000 times better than before); one part in 10 trillion accuracy over 24 hours (10 times better than before); and computes short-term stability using the Allan variance. The FMAS calibrates up to five frequency standards at one time under software control. The new service uses the Global Positioning System instead of LORAN-C, and gives time of day information as well as frequency. Subscribers to the FMAS are provided with all necessary equipment, including a 486-class computer and monitor, GPS receiver and antenna, time interval counter, modem, uninterruptible power supply, tape backup and printer. Also provided are training at NIST's Boulder, Colo., site and complete technical support for the service and equipment. The service is useful for complying with National Voluntary Laboratory Accreditation Program requirements. For more information, contact

Michael Lombardi,
Time and Frequency Division,
Boulder, Colo. 80303-3328,
(303) 497-3212,
fax: (303) 497-6461,
e-mail: (via Internet).

Media Contact: Collier Smith (Boulder),
Phone:(301) 975-NIST (6478)


NIST Guide on Measurement Uncertainty Available

In order to adopt a uniform approach to expressing uncertainty in its measurements, NIST published the first edition of its guide on measurement uncertainty in 1993. Now an updated 1994 edition of Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results is available. The 20-page guide, NIST Technical Note 1297, provides a uniform approach for expressing quantitative statements of uncertainty of NIST measurements. The approach reflects recommendations from the International Committee for Weights and Measures and the International Organization for Standardization. The 1994 edition of the guide includes a new appendix, which clarifies and gives additional guidance on a number of topics related to measurement uncertainty, including the use of certain terms such as accuracy and precision. Single copies of the 1994 edition of TN 1297 are available from the NIST Calibration Program, A104 Bldg. 411, Gaithersburg, Md. 20899-0001, (301) 975-2002, fax: (301) 926-2884. Copies also may be ordered for $17.50 prepaid from the National Technical Information Service, Springfield, Va. 22161, (703) 487-4650. Order by PB 95-143087.

Media Contact: Linda Joy,
Phone:(301) 975-NIST (6478)

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