London (GB) The Square Circle Postmarks of London 1880 - 1909
From Stamps of the World
The development of the Square Circle Postmarks of London.
In Late 1879 a new handstamp was issued to the EC Office. The trials of the Hoster Machine and style proved to be successful in using a combined date and coded handstamp.
The first Square Circles developed are also known as Geometric type cancels.