This is a computer readable catalogue of open cluster data compiled by Gosta Lynga, Lund Observatory, Box 43, S-221 00 Lund, Sweden. The present file mainly details the structure of the file "catalog"; please refer to the file "intro" for more details about the parameters. Further errors have been corrected at CDS: see below the "Historical Notes" section. A few questions still remain (see section "Problems" below)