The article treats two series. The first was issued by Fernmeldetechnischen Zentralamt (FTZ) in Darmstadt (mentioned on the intro page). These are for the BRD (3 illustrations). They were used from 1950, with the introduction of the coin telephone machine MünzFw 57. This machine accepted three coins: 10 pfennig, 50 pfennig and 1 Mark. The first illustration (7183) is for the mechanism for the Mark. Number 7184 is for the 50 pfenning while 7185 and 7186 are also for 1 Mark coins, differing only for the numbers. The author doesn't explain the numbers. My understanding is that the last two numbers (71, 73 and 74) are years in the 20th century.
The second series was issued by Deutsche Post for use in East Germany (2 illustrations). I am struggling with the countermark BDP. I think DP is for Deutsche Post, but can't explain the B.
Congratulations on having created all pages in record time. I will toast to your health tonight.
Peter