In the LINEDB offline databases, as well as in JPL and ``old'' (non-VAMDC) CDMS, the quantum numbers of the lower and upper transition levels are encoded in a character string. This appendix describes the recipe to be used for encoding. It duplicates the pages https://www.astro.uni-koeln.de/cdms/catalog and https://www.astro.uni-koeln.de/node/475 for memory.