Yugoslavia: Zeppelin airmail labels

Here is a block of 4 airmail labels from a sheet of 10. Used on Zeppelin mail.

Year: 1932, Gummed. Günter Mair's catalogue no: - YUG-C-1a, perforated 10 ¾ , sheets of 10(2x5),
intended for use on Zeppelin-mail from Yugoslavia, black/light grey-blue, 5*****