add13). An added slash "/" and an upper case letter indicates that a bass note other than the root should be played. These are called slash chords. For instance...

Simatic, Philips/Mullard/Valvo [de] Norbit, BBC Sigmatronic, ACEC Logacec, Akkord [de] Estacord, Krone Mibakron, Bistat, Datapac, Norlog, SSR, or Procontic...