As a novice postmark accumulator I was having a little trouble when sorting Zeehan and Strahan postmarks into the various types as listed in the green books (too much information and not much confidence on my part). Eventually I created this timeline summary to help quickly sort postmarks into possible types based on dates. The idea is to see start and finish dates and period of use quickly before referring to the green books for details if needed. The timeline does not replace the green books as the detail is lacking such as the limited period of use for some specific codes, how rare various codes might be etc.
Maybe other novices will find the timeline approach useful. Any errors I am happy to fix. If a nice copy is required please email for the Excel version although this was very easy to create. I should have put the Postmark type number on the Zeehan sheet as I did on the Strahan sheet. Maybe the time and date postmarks for Zeehan could be added.
The colour bar on the Strahan timelines did not scan well but I think enough can be seen to see the period covered between the start and end dates.
Comments queries or corrections welcome.