the symbol K should be used for expressing temperature intervals, dropping the former convention which expressed a temperature interval in degrees Kelvin or as abbreviated, deg K. However, the old designations are acceptable temporarily as alternatives to the new ones. One may also express temperature intervals in degrees Celsius.

(iv) Electric Current: The "ampere" is that constant current which if maintained in two straight parallel conductors of infinite length, of negligible circular sections, and placed 1 meter apart in a vacuum, would produce between these conductors a force equal to 2X10 newton per meter of length.

(v) Luminous intensity: The "candela" is the luminous intensity, in the direction of the normal, of a blackbody surface 1/600,000 square meter in area, at the temperature of solidification of platinum under a pressure of 101,325 newtons per square meter.

(c) Although the six base units, and others derived from them, are exactly defined, their practical use requires a realization through the development of accurate measurement standards. Measurement standards may be based on physical phenomena, specimen objects, signal sources, or reference instruments. Extensive theoretical studies and laboratory experiments are involved in their selection, design, construction, and operation.

(d) It will be noted that a kilogram mass standard can be calibrated only through a series of comparisons, starting from the International Prototype. The units for the other five base quantities, and all quantities derived from them, are in principle independently realizable in many laboratories. In practice, however, inevitable minor differences among instruments, environments, and operators are bound to introduce small discrepancies. Periodic comparison of standards and the resolution of these discrepancies is required for compatibility among domestic standards laboratories, as well as internationally.

(e) Within the United States, NBS consults with the major industrial and governmental standards laboratories, and cooperates with the Department of Defense and the National Conference of Standards Laboratories in conducting measurement agreement comparisons. Periodic inter-comparisons of NBS standards with those of other countries are made through the International Bu

reau of Weights and Measures, through international scientific organizations, or by direct arrangement. The operations of the International Bureau are supervised by the General Conference of Weights and Measures, to which U.S. delegates are appointed by the Department of State.

(f) Frequency and time comparisons within the United States are made by the National Bureau of Standards, the U.S. Naval Observatory, and other organizations which have an interest in precise time and frequency standards. The data from worldwide astronomical observations and from standards laboratories in many countries are coordinated by the International Bureau of the Hour, which announces recommended approximations for the rate difference between atomic and universal time. as well as for epoch adjustments.

§ 200.103 Types of calibration and test services.

(a) NBS has developed instrumentation and techniques for realizing standards for the six 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 six 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 itemized service schedules of SP 250. On those services for which fees have been established, the fees are also listed in SP 250. In cases where fees have not been fixed, services will be billed on the basis of actual costs incurred. (See § 200.116 for details relating to the description of service items and listing of fees.) Changes in services and fees are announced in supplements to SP 250 and in the monthly NBS Technical News Bulletin.1

1 For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

(c) 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 requirement to be satisfied will be helpful in determining future NBS programs. Fees for work accepted will be based upon actual costs incurred.

(d) The principal emphasis of the National Bureau of Standards is on those calibrations and other tests requiring such accuracy as can be obtained only by direct comparison with its standards. However, in order to maintain efficient utilization of specialized equipment and skilled personnel, NBS may when workload permits calibrate devices requiring lesser accuracy but suitable for working standards in plant or laboratory.

(e) Other services which may be obtainable 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.

(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 NBS.

(f) NBS 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 widely available from commercial laboratories, nor for organizations or individuals in foreign countries.

(g) Suggestions will be offered on measurement techniques and on other sources of assistance on calibration or measurement problems when the Bureau's own equipment and personnel 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 Bureau of Standards, Washington, D.C.

20234). Those which perform testing are listed in the ASTM Directory of Testing Laboratories, Commercial and Institutional. (Directory available from the American Society for Testing and Materials, 1916 Race St., Philadelphia, Pa. 19103.) Similar listings appear in buyer's guides for commercial products and in technical journals concerned with physical measurement.

[32 F.R. 21012, Dec. 29, 1967, as amended at 33 F.R. 10627, July 26, 1968]

§ 200.104 Consulting and advisory services.

(a) In areas of its special competence, the National Bureau of Standards 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.

(b) To enhance the competence of standards laboratory personnel, NBS 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 summer course in electromagnetic measurements and standards is conducted periodically by the NBS Radio Standards Laboratory at Boulder, Colorado.

§ 200.105 Standard reference materials.

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 standardized specimen or a substance of certified composition, properties, or purity. Types of such specimens are listed in several of the detailed fee schedules in SP 250. For information regarding carefully characterized materials see Subchapter B of Chapter II of this Title 15. The Office of Standard Reference Materials in the NBS Institute for Materials Research 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.

[32 F.R. 21012, Dec. 29, 1967, as amended at 33 F.R. 10627, July 26, 1968]

§ 200.106 Critically evaluated data.

Data on the physical properties of the thousands of well-defined substances which are commercially available need to be compiled and evaluated to be useful for reference in engineering design. The Office of Standard Reference Data in the NBS Institute for Basic Standards provides two-way communication with a number of governmental and nongovernmental data centers throughout the country. Its present compilation and dissemination activities cover seven technical areas-nuclear data, atomic and molecular data, solid state data, thermodynamic and transport data, chemical kinetics, colloid and surface properties, and mechanical properties. Accounts of progress appear in the National Standard Reference Data System News (available upon request from the Office of Standard Reference Data) and in the monthly NBS Technical News Bulletin.1

§ 200.107 Publications.

(a) Changes in services and fees, as published in the supplements to SP 250, appear also in the monthly NBS Technical News Bulletin.' The Bulletin also describes recent results of Bureau staff work, lists currently issued publications, and carries sections giving up-to-date detailed information on standards and calibrations, standard reference materials, seminar announcements, conference summaries, and the National Standard Reference Data System. An index to publications by the Bureau authors will be found in Supplements to Special Publication 240, Publications of the National Bureau of Standards. This index covers the publication series of Monographs,' and Technical Notes,' and includes all papers appearing either in the NBS Journal of Research or in outside technical journals.

1

(b) U.S. Government Research and Development Reports, a semimonthly announcement journal covering over 1,000 new documents per issue, is sold by the NBS Clearinghouse for Federal Scientific and Technical Information, Springfield, Va. 22151. Other CFSTI series available on subscription include the USGRDR In

1 For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

(a) Technical services. The National Bureau of Standards radio stations WWV at Fort Collins, Colo., 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, 20, and 25 MHz (WWV) and 2.5, 5, 10, 15, and 20 MHz (WWVH); (2) standard time signals; (3) time intervals; (4) UT1 corrections; (5) standard audio frequencies; (6) standard musical pitch; (7) a slow time code; (8) propagation forecasts; (9) geophysical alerts; and (10) storm warnings. The NBS also broadcasts time and frequency signals from its low frequency station, WWVB, also located at Fort Collins, Colo.

(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 72 seconds before the minute. Greenwich mean time (sometimes referred to as UT) is used in these announcements. The actual time scale is known as coordinated universal time (UTC).

(c) Time corrections. The UTC time scale operates on atomic frequency, but by means of step adjustments is made to approximate the astronomical UT1 scale. It may disagree from UT1 by as much as 0.7 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 0.7 second, a correction to UTC is encoded by the use of double ticks after the start of each minute. The first through the seventh seconds ticks

will indicate a "plus" correction, and from the ninth through the 15th a "minus" correction (the eighth is not used). 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 millisecond second pulses occur within a 40millisecond 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) (not offset as in the past). 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 NBS atomic frequency standards, which realize the internationally defined cesium resonance frequency with an accuracy of 2 parts in 1012. The frequencies transmitted by WWV and WWVH are held stable to better than ±2 parts in 10 at all times. Deviations at WWV are normally less than 1 part in 1012 from day to day. Incremental frequency adjustments not exceeding 1 part in 10" are made at WWV as necessary. Frequency adjustments made at WWVH do not exceed 2 parts in 10". 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) Propagation forecasts. These occur in voice at the 14th minute of each hour from WWV. They are short-term forecasts of propagation conditions along North Atlantic paths such as Washington, D.C., to London, England, along with a description of current geomagnetic activity, and are provided by the Telecommunications Services Center, Office of Telecommunications, Boulder, Colo. 80302. The format consists of the statement: "The radio propagation quality forecast at (one of the following times: 0100, 0700, 1300, or 1900 UT) is ." (one of the following adjectives: Excellent, very good, good, fair to good, fair, poor to fair, poor, very poor, or useless). This statement is followed by: "Current geomagnetic activity is (one of the following characterizations: Quiet, unsettled, or disturbed).

(i) Geophysical alerts. These occur in voice at the 18th minute of each hour from WWV and at the 45th minute from WWVH. They point out outstanding events which are in process, followed by a summary of selected solar and geophysical events in the past 24 hours. They are provided by the Space Environment Laboratory, National Oceanic and Atmospheric Administration, Boulder, Colo. 80302.

(j) Storm information. These will cover the waters of the Atlantic from WWV and the Pacific from WWVH and are given at the 10th and 12th minute of each hour from WWV and at the 49th and 51st minute of each hour from WWVH. Times of issue are 0500, 1100, 1600, and 2300 UT from WWV, and 0000, 0600, 1200, and 1800 UT from WWVH. They are prepared by the National Weather Service, Silver Spring, Md. 20910.

(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 50th minute on WWV.

(1) 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 UT1 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" per day.

(m) WWVL. This station (antenna coordinates 40°40'51.3'' N., 105°03'00.0'' W.; radiated power 2 kw.) usually broadcasts on 19.9 and 20.0 kHz. Effective 0000 hours UTC, July 1, 1972, all transmissions were curtailed, and depending upon need, this station will broadcast on an experimental and intermittent basis only.

(n) Special Publication 236. This publication describes in detail the standard frequency and time service of the National Bureau of Standards. Single copies may be obtained upon request from the National Bureau of Standards, Boulder, Colo. 80302. Quantities may be obtained from the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402, at 15 cents per copy. [37 F.R. 28895, Dec. 30, 1972]

§ 200.109 Request procedure.

(a) A formal purchase order for the calibration or test should be sent before or at the time the instrument or standard is shipped. This 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 his equipment is out of service, he can usually arrange to delay shipment until the test is scheduled to start. (See § 200.111.) 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 section 200.114 below. Acceptance of purchase orders does not imply acceptance of any provisions set forth in the order contrary to the policy, practice, or regulations of the National Bureau of Standards or the U.S. Government. (A statement to the effect that the National Bureau of Standards 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 the Bureau 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, the Bureau will mark the piece with an NBS identification number. If the apparatus submitted has been previously calibrated by the Bureau, 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 related to electrical standards in the radio frequency region (above 30 kHz) or to frequency and time standards should be directed to:

Coordinator, Calibration Services, Radio Standards Laboratory, National Bureau of Standards, Boulder, Colo. 80302.

(e) Inquiries for measurement services other than those noted in paragraph (d) of this section, should be directed to the NBS address listed in the various sections of SP 250, or to:

Test Administration Unit, National Bureau of Standards, Washington, D.C. 20234. [32 F.R. 21012, Dec. 29, 1967, as amended at 33 F.R. 10627, July 26, 1968]

§ 200.110 Shipping, insurance, and risk of loss.

(a) Shipment of apparatus to NBS 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 NBS will not under