Hi EMaxim,
Answers were perfect from other members. From the same era as the OP thread, it was the way they were doing it in Germany and for a long period as per cupram's Allied Control booklet.
Here two others from the same cover as the 5 Pfg which is a foreign rate to England for normal letter. Franking (From may be 3 different booklet) at 80 Pfg from inflation Rate Period 5 (6.5.1920-31.3.1921)
Hornet

