Mechanical Calculators: German Citipost Stamp Sheet Validity

Hello

One of my thematic interests is mechanical calculators (pre computer).

The German CitiPost has a striking stamp sheet on this theme - Leibniz who made one of the first calculators, see below.

I notice no search in the forum sections brings up CitiPost. As far as can gather they are a postal firm running in parallel to Deutsche Post but wasn't clear if they were formally catalogued and valid thematics. (Although not bothered about their formality as they are attractive and interesting.)

delcampe.net brings up 150+ stamps for CitiPost at present on various themes they have published.

Thanks for any insight.

regards
David

CitiPost I believe is Berlin's own postal system. Berlin is where the Leibniz library is located.

I think CitiPost is a UK based parcel delivery service with offices in Germany. As far as I know Deutsche Post still handles letter delivery in Berlin. The Leibniz Bibliothek is located in Hannover.

Robert

P.S. I did a quick internet search for CitiPost and discovered they also deliver letters and post cards throughout Germany, not just parcels. Their website states their rates are better than Deutsche Post.