PART IV
                                   SERIES B AND C RECOMMENDATIONS
                                      SERIES B RECOMMENDATIONS
                                        Means of expression
         Recommendation
             No.                                           Title
             B.1     Letter symbols for telecommunications
             B.3     Use of the international system of units (SI)
             B.10    Graphical symbols and rules for the preparation of  documentation  in
         telecommunications
             B.11    Legal time; use of the term UTC
             B.12    Use of the decibel and the neper
             B.13    Terms and definitions
             B.14    Terms and symbols for information quantities in telecommunications
             B.15     Nomenclature  of  the  frequency  and  wavelength  bands   used   in
         telecommunications
             B.16    Use of certain terms linked with physical quantities
             B.17    Adoption of the CCITT Specification and Description Language (SDL)
             B.18    Traffic intensity unit
             B.19    Abbreviations and initials used in telecommunications
         Recommendation B.11) 
                                    LETTER SYMBOLS FOR TELECOMMUNICATIONS
               The CCITT,
         considering
               (a) that in order  to  simplify  the  reading  of  documents  dealing  with
         telecommunication technique, it  is  essential  to  use  simple  notations  in  a
         homogeneous system and having well-defined meaning;  that,  moreover,  it  is  an
         advantage, wherever possible,  to  have  notations  that  have  been  universally
         adopted;
               (b) that CMV is collaborating with Technical Committee No. 25 of the IEC,
         recommends
               that in their mutual  relations  the  ITU  and  its  permanent  organs  and
         Administrations and recognized private operating agencies use in  all  languages,
         wherever possible, the letter  symbols  and  the  notations  recommended  by  the
         International  Organization  for  Standardization  (ISO)  and  the  International
         Electrotechnical Commission (IEC) to represent the physical  quantities  and  the
         mathematical operations.
               Note - References of relevant publications (updated in 1988).
               ISO Standard 31:  "General  principles  concerning  quantities,  units  and
         symbols"
               Parts of ISO Standard 31 of greatest interest for telecommunications:
               0          (General principles)
               I          (Quantities and units of space and time)
               II         (Quantities and units of periodic and related phenomena)
               V          (Quantities and units of electricity and magnetism)
               VI         (Quantities and units  of  light  and  related  electromagnetic
                  radiations)
               VII        (Quantities and units of acoustics)
               XI         (Mathematical signs and symbols)
               IEC Publication 27: "Letter symbols to be used in electrical technology"
               27-1   General  (1971 Edit. 5, with 1974 Amend. 1 and 1977 Amend. 2) (1983 
                              Amend. 4, including 1981 Amend. 3)
               27-1A  (1976)      (Time-dependent quantities)
               27-2   (1972)      (Telecommunications and electronics)
               27-2A  (1975)      (First  supplement:  waveguide  propagation;  scattering
                              matrix and transfer matrix;  static  convectors;  automatic
                              control science and technology)
               27-2B  (1980)      (Second supplement: linear n-port networks)
               27-3    (1974)       (Logarithmic   quantities   and   units)   (see   CCIR
         Recommendation 574)
               27-4   (1985)      (Quantities to be used for rotating electric machines)
               See also IEC Handbook Letter Symbols (1983) and the  Directives  applicable
               to the work of the IEC on letter Symbols (1986).


         1)      A similar text will be submitted to the CCIR as a revision of Rec. 608.



         Fascicle I.3 - Rec. B.1                   PAGE1