MARC21       008m'18  Frequency [obs.]
     Values: 
              #   No determinable frequency [obs.]
              a   Annual [obs.]
              b   Bimonthly [obs.]
              c   Semiweekly [obs.]
              d   Daily [obs.]
              e   Biweekly [obs.]
              f   Semiannual [obs.]
              g   Biennial [obs.]
              h   Triennial [obs.]
              i   Three times a week [obs.]
              j   Three times a month [obs.]
              m   monthly [obs.]
              n   Not applicable [obs.]
              q   Quarterly [obs.]
              s   Semimonthly [obs.]
              t   Three times a year [obs.]
              u   Unknown [obs.]
              w   Weekly [obs.]
              z   Other frequencies [obs.]