(a) The National Institute of Standards & Technology (NIST) has been assigned the following functions (15 U.S.C. 271 et seq.):

(1) The custody, maintenance, and development of the national standards of measurement, and the provision of means and methods for making measurements consistent with those standards, including the comparison of standards used in scientific investigations, engineering, manufacturing, commerce, and educational institutions with the standards adopted or recognized by the Government.

(2) The determination of physical constants and properties of materials when such data are of great importance to scientific or manufacturing interests and are not to be obtained with sufficient accuracy elsewhere.

(3) The development of methods for testing materials, mechanisms, and structures, and the testing of materials, supplies, and equipment, including items purchased for use of Government departments and independent establishments.

(4) Cooperation with other governmental agencies and with private organizations in the establishment of standard practices, incorporated in codes and specifications.

(5) Advisory service to Government agencies on scientific and technical problems.

(6) Invention and development of devices to serve special needs of the Government.

(b) The calibration and testing activities of NIST stem from the functions in paragraphs (a) (1) and (3) of this section. NIST provides the central basis within the United States for a complete and consistent system of measurement; coordinates that system, and the measurement systems of other nations; and furnishes essential services leading to accurate and uniform physical measurements throughout this Nation's scientific community, industry, and commerce.

(c) The provision of standard reference materials for sale to the public is assigned to the Office of Standard Reference Materials of the National Measurement Laboratory, NIST. That Office evaluates the requirements of science and industry for carefully characterized reference materials, stimulates efforts of NIST to develop methods for production of needed reference materials and directs their production and distribution. For further information on standard reference materials see Subchapter B, Chapter II, Part 230, of this title.

(a) The NIST staff continually reviews the advances in science and the trends in technology, examines the measurement potentialities of newly discovered physical phenomena, and uses these to devise and improve standards, measuring devices, and measurement techniques. As new requirements appear, there are continual shifts of program emphasis to meet the most urgent needs for the measurement of additional quantities, extended ranges, or improved accuracies.

(b) The basic research and development activities of NIST are primarily funded by direct appropriations, and are aimed at meeting broad general needs. NIST may also undertake investigations or developments to meet some specialized physical measurement problem of another Government agency, industrial group, or manufacturing firm, using funds supplied by the requesting organization.

(a) NIST has developed instrumentation and techniques for realizing standards for the seven base units of the International System of Units, as agreed upon by the General Conference of Weights and Measures. Reference standards have been established not only for these seven base units, but also for many derived quantities and their multiples and submultiples. Such reference standards, or equivalent working standards, are used to calibrate laboratory and plant standards for other organizations. Accuracy is maintained by stability checks, by comparison with the standards of other national and international laboratories, and by the exploration of alternative techniques as a means of reducing possible systematic error.

(b) Calibrations for many types of instruments and ranges of physical quantities are described in the NIST Special Publication 250 (SP 250). (See § 200.115 for details relating to the description of service items and listing of fees.)

(c) In recent years NIST has offered to the public new measurement services called measurement assurance programs. These programs are designed for laboratories whose measurement process involves the calibration of other standards. A measurement assurance program is a measurement quality control process. By use of carefully designed redundant measurements and measurements made on NIST transport standards a total uncertainty of the laboratories measurement process can be determined by NIST. The results of these tests are then reported to the customer as uncertainties of the customer's measurements relative to national standards.

(d) Special measurements not listed in SP 250 may be made upon request. These might involve unusual physical quantities, upper or lower extremes of range, higher levels of accuracy, fast response speeds, short durations, broader ranges of associated parameters, or special environmental conditions. Such inquiries should describe clearly the measurement desired. Indication of the scientific or economic basis for the requirements to be satisfied will be helpful in determining future NIST programs. Fees for work accepted will be based upon actual costs incurred.

(e) The principal emphasis of NIST is on those calibrations and other tests requiring such accuracy as can be obtained only by direct comparison with its standards.

(f) Other services which may be obtained include:

(1) Tests of measuring instruments to determine compliance with specifications or claims, when the evaluation is critical in national scientific or technical operations, and when suitable facilities are not available elsewhere; and

(2) Referee tests in important cases when clients are unable to agree upon the method of measurement, the results of tests, or the interpretation of these results, but have agreed in advance in writing to accept and abide by the findings of NIST.

(g) NIST reserves the right to decline any request for services if the work would interfere with other activities deemed by the Director to be of greater importance. In general, measurement services are not provided when available from commercial laboratories.

(h) Suggestions will be offered on measurement techniques and on other sources of assistance on calibration or measurement problems when the equipment and personnel of NIST are unable to undertake the work. The National Conference of Standards Laboratories issues a Directory of Standards Laboratories in the United States which perform calibration work (obtainable from NCSL Secretariat, c/o National Institute of Standards & Technology, Boulder, CO 80303). Those laboratories which perform testing are listed in the ASTM Directory of Testing Laboratories, Commercial and Institutional. (Directory available from the Amercian Society for Testing and Materials, 1916 Race Street, Philadelphia, PA 19103.) Similar listings appear in buyer's guides for commercial products and in technical journals concerned with physical measurement.

(a) In areas of its special competence, NIST offers consulting and advisory services on various problems related to measurement, e.g., details of design and construction, operational aspects, unusual or extreme conditions, methods of statistical control of the measurement process, automated acquisition of laboratory data, and data reduction and analysis by computer. Brief consultation may be obtained at no charge; the fee for extended effort will be based upon actual costs incurred. The services outlined in this paragraph do not include services in connection with legal proceedings not involving the United States as a named party, nor to testimony or the production of data, information, or records in such legal proceedings which is governed by the policies and procedures set forth in Subchapter H, Chapter II, Part 275, of this title.

(b) To enhance the competence of standards laboratory personnel, NIST conducts at irregular intervals several group seminars on the precision measurement of specific types of physical quantities, offering the opportunity of laboratory observation and informal discussion. A brochure describing the current series of seminars can be obtained by writing the Office of Measurement Services, National Institute of Standards & Technology, Washington, DC 20234.

Often the performance of a device or structure can be evaluated at the user's laboratory by comparing its response to unknown materials with its response to a stable, homogeneous reference specimen which has been well-characterized with regard to the physical or chemical property being measured. For information regarding carefully characterized materials see Subchapter B, Chapter II, Part 230, of this title. The Office of Standard Reference Materials in the NIST National Measurement Laboratory administers a program to provide many types of well-characterized materials that are needed to calibrate a measurement system or to produce scientific data that can be readily referred to a common base. NIST SP 260 is a catalog of Standard Reference Materials available from NIST.

Data on the physical and chemical properties of the large variety of substances used in science and technology need to be compiled and evaluated for application in research, development, engineering design, and commerce. The Office of Standard Reference Data (OSRD) in the NIST National Measurement Laboratory provides coordination of and access to a number of governmental and nongovernmental data centers throughout this country and the world which are responsive to user needs for data. The OSRD's present program is assembled under a series of tasks which include data for application in energy, environment and health, industrial process design, materials durability, and resource recovery. The subject data are disseminated as hard-copy information in the Journal of Physical and Chemical Reference Data, published jointly with the American Chemical Society and the American Institute of Physics, in the National Standard Reference Data System reports as the NSRDS-NIST series, and as NIST special reports. Magnetic tapes of data on selected topics are also issued through the OSRD and the National Technical Information Service. A newsletter, “Reference Data Report,” is issued bimonthly describing current activities. Information concerning the above is available upon request from the OSRD.

Publications provide the primary means of communicating the results of the NIST programs and services to its varied technical audiences, as well as to the general public. NIST issues some fifteen categories of publications including three periodicals, ten non-periodicals series, interagency reports, and papers in the journals and books of professional organizations, technological associations, and commercial publications. The calibration services, standard reference materials and related measurement services along with changes and fees are published in two Special Publications (SP's) and their supplements. These are SP 250 “Calibration and Related Measurement Services of the National Institute of Standards & Technology” 1 and SP 260 “NIST Standard Reference Materials Catalog.” 1 A complete catalog of all publications by NIST authors is issued annually as a supplement to SP 305 “Publications of the National Institute of Standards & Technology.” Announcements and listings of recent NIST publications and services are published in each issue of the bimonthly “NIST Journal of Research” 2 and the NIST monthly magazine, “Dimensions/NIST” 2. Complete citations to NIST publications, along with information on availability are published bimonthly in the “NIST Publications Newsletter”, available free from the Technical Information and Publications Division, National Institute of Standards & Technology, Washington, DC 20234. NIST publications are also announced (with abstracts) in “Government Reports Announcements and Index” published every two weeks by the National Technical Information Service (NTIS), Springfield, Virginia 22161 3 . NTIS also sells microfiche copies of all NIST GPO-published documents, as well as paper copy and microfiche versions of NIST Interagency Reports.

(a) Technical services. The NIST radio stations WWV at Fort Collins, Colorado, and WWVH on the island of Kauai, Hawaii, broadcast a number of technical services continuously night and day. These services are:

(1) Standard radio frequencies, 2.5, 5, 10, 15, and 20, MHz (WWV) and 2.5, 5, 10, and 15 MHz (WWVH); (2) standard time signals; (3) time intervals; (4) UTI corrections; (5) standard audio frequencies; (6) standard musical pitch; (7) a slow time code; (8) Omega Navigation System status reports; (9) geophysical alerts; and (10) marine storm warnings. NIST also broadcasts time and frequency signals from its low frequency station, WWVB, also located at Fort Collins, Colorado.

(2) [Reserved]

(b) Time announcements. Once per minute voice announcements are made from WWV and WWVH. The two stations are distinguished by a female voice from WWVH and a male voice from WWV. The WWVH announcement occurs first, at 15 seconds before the minute, while the WWV announcement occurs at 7 1/2 seconds before the minute. Coordinated Universal Time (UTC) is used in these announcements.

(c) Time corrections. The UTC time scale operates on atomic frequency, but by means of step adjustments is made to approximate the astronomical UTI scale. It may disagree from UTI by as much as 0.9 second before step adjustments of exactly 1 second are made. These adjustments, or leap seconds are required about once per year and will usually be made on December 31 or June 30. For those who need astronomical time more accurately than 0.9 second, a correction to UTC is encoded by the use of double ticks after the start of each minute. The first through the eighth seconds ticks will indicate a “plus” correction, and from the ninth through the 16th a “minus” correction. The correction is determined by counting the number of double ticks. For example, if the first, second, and third ticks are doubled, the correction is “plus” 0.3 second. If the ninth, 10th, 11th, and 12th ticks are doubled, the correction is “minus” 0.4 second.

(d) Standard time intervals. An audio pulse (5 cycles of 1000 Hz on WWV and 6 cycles of 1200 Hz on WWVH), resembling the ticking of a clock, occurs each second of the minute except on the 29th and 59th seconds. Each of these 5-millisecond second pulses occur within a 40-millisecond period, wherein all other modulation (voice or tone) is removed from the carrier. These pulses begin 10 milliseconds after the modulation interruption. A long pulse (0.8 second) marks the beginning of each minute.

(e) Standard frequencies. All carrier and audio frequencies occur at their nominal values according to the International System of Units (SI). For periods of 45-second duration, either 500-Hz or 600-Hz audio tones are broadcast in alternate minutes during most of each hour. A 440-Hz tone, the musical pitch A above middle C, is broadcast once per hour near the beginning of the hour.

(f) Accuracy and stability. The time and frequency broadcasts are controlled by the NIST atomic frequency standards, which realize the internationally defined cesium resonance frequency with an accuracy of 1 part in 10 13. The frequencies transmitted by WWV and WWVH are held stable to better than ±2 parts in 10 11 at all times. Deviations at WWV are normally less than 1 part in 10 12 from day to day. Incremental frequency adjustments not exceeding 1 part in 10 12 are made at WWV and WWVH as necessary. Changes in the propagation medium (causing Doppler effect, diurnal shifts, etc.) result in fluctuations in the carrier frequencies as received which may be very much greater than the uncertainties described above.

(g) Slow time code. A modified IRIG H time code occurs continuously on a 100-Hz subcarrier. The format is 1 pulse per second with a 1-minute time frame. It gives day of the year, hours, and minutes in binary coded decimal form.

(h) Omega announcements. Omega Navigation System status reports are broadcast in voice from WWV at 16 minutes after the hour and from WWVH at 47 minutes after the hour. The international Omega Navigation System is a very low frequency (VLF) radio navigation aid operating in the 10 to 14 kHz frequency band. Eight stations are in operation around the world. Omega, like other radio navigation systems, is subject to signal degradation caused by ionospheric disturbances at high latitudes. The Omega announcements on WWV and WWVH are given to provide users with immediate notification of such events and other information on the status of the Omega system.

(i) Geophysical alerts. These occur in voice at the 18th minute of each hour from WWV. They point out outstanding events which are in process, followed by a summary of selected solar and geophysical events in the past 24 hours and a forecast for the next 24 hours. They are provided by the Space Environment Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO 80303.

(j) Marine storm information. Weather information about major storms in the Atlantic and eastern North Pacific are broadcast in voice from WWV at 8, 9, and 10 minutes after each hour. Similar storm warnings covering the eastern and central North Pacific are given from WWVH at 48, 49, and 50 minutes after each hour. An additional segment (at 11 minutes after the hour on WWV and at 51 minutes on WWVH) may be used when there are unusually widespread storm conditions. The brief messages are designed to tell mariners of storm threats in their areas. If there are no warnings in the designated areas, the broadcasts will so indicate. The ocean areas involved are those for which the U.S. has warning responsibility under international agreement. The regular times of issue by the National Weather Service are 0500, 1100, 1700, and 2300 UTC for WWV and 0000, 0600, 1200, and 1800 UTC for WWVH. These broadcasts are updated effective with the next scheduled announcement following the time of issue.

(k) “Silent” periods. These are periods with no tone modulation during which the carrier, seconds ticks, minute time announcements, and 100 Hz modified IRIG H time code continue. They occur during the 16th through the 20th minute on WWVH and the 46th through the 51st minute on WWV.

(l) WWVB. This station (antenna coordinates 40°40′28.3″ N., 105°02′39.5″ W.; radiated power 12 kw.) broadcasts on 60 kHz. Its time scale is the same as for WWV and WWVH, and its frequency accuracy and stability are the same. Its entire format consists of a 1 pulse per second special binary time code giving minutes, hours, days, and the correction between its UTC time scale and UTI astronomical time. Identification of WWVB is made by its unique time code and a 45° carrier phase shift which occurs for the period between 10 minutes and 15 minutes after each hour. The useful coverage area of WWVB is within the continental United States. Propagation fluctuations are much less with WWVB than with high-frequency reception, permitting frequency comparisons to be made to a few parts in 10 11 per day.

(m) Special Publication 432. This publication describes in detail the standard frequency and time service of NIST. Single copies may be obtained at no charge upon request from the National Institute of Standards & Technology, Time & Frequency Services Group, 524.06, Boulder, CO 80303. Quantities may be obtained from the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402, at a nominal charge per copy.

(a) A formal purchase order for the calibration or test should be sent before or at the time the instrument or standard is shipped. The purchase order should provide clear identification of the apparatus being submitted, and give separate instructions for return shipment, mailing of report, and billing. If a customer wishes to minimize the time during which the equipment is out of service, the customer can usually arrange to be notified of the scheduled test date to allow timely shipment. (See § 200.110.) Requests from Federal agencies, or from State agencies, for calibrations or tests on material to be used on private or Federal contract work should be accompanied either by purchase order or by letter or document authorizing the cost of the work to be billed to the agency.

(b) The submission of a purchase order for measurement services under this subchapter shall be understood as constituting an agreement on the part of the customer to be bound by the restrictions on the use of results as set forth in § 200.113 of this part. Acceptance of purchase orders does not imply acceptance of any provisions set forth in the order contrary to the policy, practice, or regulations of NIST or the U.S. Government. (A statement to the effect that NIST is an agency of the U.S. Government should satisfy other Government agencies with regard to compliance with Government regulations and Executive orders.)

(c) A test number will be assigned by NIST to each instrument or group of similar instruments or standards when the order is accepted. This test number should be referred to in all subsequent communications. Also, each instrument in a group must be uniquely identified, usually by the manufacturer's name and instrument serial number. When the serial number is lacking, an alternative identifying mark should be provided. If none is found, NIST will mark the piece with an NIST identification number. If the apparatus submitted has been previously calibrated by NIST, the serial number or identifying mark should be given on the new order, so that a continuing record of stability history can be established.

(d) Inquiries for measurement services should be directed to the NIST address listed in the various sections of the Appendix to SP 250.

(a) Shipment of apparatus to NIST for calibration or other test should be made only after the customer has accepted the estimate of cost and the tentative scheduling. Repairs and adjustments on apparatus submitted should be attended to by the owner, since NIST will not undertake them except by special arrangement. Apparatus not in good condition will not be calibrated. If defects are found after calibration has begun, the effort may be terminated, a report issued summarizing such information as has been found, and a fee charged in accordance with the amount of work done.

(b) The customer should pack apparatus sent to NIST so as to minimize the likelihood of damage in shipment and handling. Suggestions on packing and shipping are made in some sections of SP 250. In every case, the sender should consider the nature of the apparatus, pack it accordingly, and clearly label shipments containing fragile instruments or materials, such as glass and the like.

(c) To minimize damage during shipment resulting from inadequate packing, the use of strong reusable containers is recommended. As an aid in preventing loss of such containers, the customer's name should be legibly and permanently marked on the outside. In order to prolong the container's use the notation “REUSABLE CONTAINER, DO NOT DESTROY” should be marked on the outside.

(d) Shipping and insurance coverage instructions should be clearly and legibly shown on the purchase order for the calibration or test. The customer must pay shipping charges to and from NIST; shipments from NIST will be made collect. The method of return transportation should be stated, and it is recommeded that return shipments be insured, since NIST will not assume liability for their loss or damage. For long-distance shipping it is found that air express and air freight provide an advantage in reduction of time in transit. If return shipment by parcel post is requested or is a suitable mode of transportation, shipments will be prepaid by NIST, but without covering insurance. When no shipping or insurance instructions are furnished, return shipment will be made by common carrier collect, but uninsured.

(e) NIST will not be responsible for the risk of loss or damage to any item during shipment to or from NIST. Any arrangements for insurance covering this risk must be made by the customer. Return shipment will be made by NIST as indicated in paragraph (d) of this section. The purchase order should always show the value of the equipment, and if transit insurance is carried by the customer, this fact should be stated.

(f) The risk of loss or damage in handling or testing of any item by NIST must be assumed by the customer, except when it is determined by NIST that such loss or damage was occasioned solely by the negligence of NIST personnel.

(g) When a test number has been assigned prior to shipment to NIST, this number should be clearly marked on the shipping container. When a test number has not been assigned, an invoice, copy of the purchase order, or letter should be enclosed in the shipment to insure proper identification. The original purchase order should be forwarded as appropriate to:

(h) The calibrations listed in SP 250 are performed at Boulder, Colorado and Gaithersburg, Maryland.

Schedule work assignments for calibrations and other tests will generally be made in the order in which confirmed requests are received. However, Government work may be given priority. On the regular services, the workload is usually such that the turn-around interval, between the date a customer's apparatus is received and the date it is prepared for return shipment, will be not more than 45 days. Some types of instruments may require considerably longer, particularly if their abnormal behavior requires reruns to check reliability. The customer who can spare the instrument for only a short time can usually arrange by letter or telephone call for shipping it to NIST just as the assigned starting date approaches. A notice will be sent acknowledging receipt of the customer's standard and/or purchase order. If both a confirmed purchase order (or equivalent) and the apparatus have been received, estimates of the completion date and the calibration fee will be sent upon request.

NIST welcomes scientists and engineers who may wish to visit its laboratories and discuss its methods. Ordinarily visitors will not be permitted to witness the actual carrying out of highly precise measurements because their presence introduces distraction that may lead to errors or delays. This policy may be waived in those cases where NIST determines that the visitor can be of service in setting up apparatus of a new or unusual nature, in the case of referee tests, or in other cases in which the legal validity of the result may require the presence of duly authorized witnesses.

(a) Results of calibrations and other tests are issued to the customer as formal reports entitled, “National Institute of Standards & Technology Report of Calibration,” “National Institute of Standards & Technology Report of Test,” or “National Institute of Standards & Technology Report of Analysis,” as appropriate. Copies are not supplied to other parties except under applicable Federal law. Whenever formal certification is required by law, or to meet special conditions adjudged by NIST to warrant it, a letter will be provided certifying that the particular item was received and calibrated or tested, and identifying the report containing the results.

(b) NIST reports of calibration generally include in sentence form a statement of the uncertainty attached to the numerical values reported. Limits of uncertainty usually comprise an estimate of systematic error plus a value of imprecision. Details on how these estimates are arrived at are in many cases included in the calibration report. Additional information may be found in SP 250.

(c) The NIST practice is to express data given in calibration or test reports in the SI or International System of Units. The International System of Units (SI) was defined and given official status by the 11th General Conference of Weights and Measures, 1960. A complete listing of SI units is presented in detail in NIST SP 330. The NIST will express data in SI units unless this makes communication excessively complicated. For example, commercial gage designations, commonly used items identified by nominal dimensions, or other commercial nomenclatures or devices (such as drill sizes, or commercial standards for weights and measures) expressed in customary units are an exception from this practice. However, even in such instances, when practical and meaningful, SI and customary units may be given in parallel. Users of NIST calibration services may specify the units to be used in the calibration, especially for commercial devices and standards using customary units or units having some legal definition.

(a) As the national standards laboratory of the United States, NIST maintains and establishes the primary standards from which measurements in science and industry ultimately derive. It is therefore sometimes desirable for manufacturers or users of measurement standards to make appropriate reference to the relationship of their calibrations to NIST calibrations. The following considerations must be borne in mind, and shall be understood as constituting an agreement on the part of the NIST customer to be bound thereby in making reference to NIST calibration and test reports.

(b) The results of calibrations and tests performed by NIST are intended solely for the use of the organization requesting them, and apply only to a particular device or specimen at the time of its test. The results shall not be used to indicate or imply that they are applicable to other similar items. In addition, such results must not be used to indicate or imply that NIST approves, recommends, or endorses the manufacturer, the supplier, or the user of such devices or specimens, or that NIST in any way “guarantees” the later performance of items after calibration or test.

(c) NIST declares it to be in the national interest that it maintain an impartial position with respect to any commercial product. Advertising the findings on a single instrument could be misinterpreted as an indication of performance of other instruments of identical or similar type. There will be no objection, however, to a statement that the manufacturer's primary standards have been periodically calibrated by NIST, if this is actually the case, or that the customer might arrange to have NIST calibrate the item purchased from the manufacturer.

(d) NIST does not approve, recommend, or endorse any proprietary product or proprietary material. No reference shall be made to NIST, or to reports or results furnished by NIST in any advertising or sales promotion which would indicate or imply that NIST approves, recommends, or endorses any proprietary product or proprietary material, or which has as its purpose an intent to cause directly or indirectly the advertised product to be used or purchased because of NIST test reports or results.

(a) In accordance with 15 U.S.C. 271 et seq., fees are charged for all measurement services performed by NIST, unless waived by the Director, or the Director's designee, when deemed to be in the interest of the Government. The above-mentioned statutes authorize the issuance from time to time of appropriate regulations regarding the payment of fees, the limits of tolerance on standards submitted for verification, and related matters.

(b) The minimum fee for any service request accepted by NIST is $10, unless otherwise indicated in SP 250. If apparatus is returned without testing, a minimum charge of $10 may be made to cover handling. Charges commensurate with the work performed will be assessed for calibrations which cannot be completed because of faulty operation of the customer's device. Fees for calibrations or tests include the cost of preparation of an NIST report. Remittances should be made payable to the National Institute of Standards & Technology.

(a) NIST Special Publication 250, “Calibration and Related Measurement Services of the National Institute of Standards & Technology” is hereby incorporated by reference, pursuant to 5 U.S.C. 552(a)(1) and 1 CFR Part 51. SP 250 states the authority under which NIST performs various types of measurement services including calibrations and tests and charges fees therefor, states the general conditions under which the public may secure such services, decribes these services in considerable detail, and lists the fees to be charged, and sets out the instructions for requesting them in an appendix which is reviewed, revised and reissued semi-annually (December and June). The Director, Office of the Federal Register, approved the incorporation by reference on December 28, 1967.

(b) SP 250 is available at the following places:

(1) Superintendent of Documents, Government Printing Office, Washington, DC 20402.

(2) Technical Information and Publications Division, National Institute of Standards & Technology, Washington, DC 20234.

(3) District Offices of the U.S. Department of Commerce.

(4) Federal Depository Libraries.

(c) Revisions of SP 250 will be issued from time to time by the National Institute of Standards & Technology, Washington, DC 20234.

(d) Further information concerning policies, procedures, services, and fees may be obtained by writing the Office of Measurement Services, National Institute of Standards & Technology, Washington, DC 20234.