Where does “sechs” come from?

sechs (Translingual) comes from German sechs, from Middle High German sehs, from Old High German sehs, from Proto-West Germanic sehs, from Proto-Germanic sehs, from Proto-Indo-European swéḱs — six.

sechs (Translingual): Spoken by a player during a match with one or more visually impaired players to indicate the sixth rank in algebraic notation