
Great Britain Post Office Numbers – http://www.gbps.org.uk/information/po-numbers/index.php
This resource is provided by the Great Britain Philatelic Society
In the listings here, the offices are listed in numeric order, together with the county, and in the England and Wales list the approximate date that the office was allocated that number (as taken from various Post Office listings). If more than one office is listed (other than sub-offices of the same head office), it means that the number was reallocated. If a range of dates is listed, they represent the first and last official lists in which the allocation of the number to that office appears.
The 4-Bar Postmarks for the USPS – http://www.postmarks.org/resources/PMCC_FourBarCancelsUSPS.pdf
This resource is provided by the Postmark Collectors Club
What Is My Postmark Worth – http://www.postmarks.org/resources/Value-of-Postmarks.pdf
This resource is provided by the Postmark Collectors Club
The Postmarks of the British IslesFrom 1840 to 1876 – http://www.gbps.org.uk/information/downloads/files/postal-markings/The%20History%20of%20the%20Postmarks%20of%20the%20British%20Isles%20from%201840%20to%201876%20-%20John%20Hendy%20(1909).pdf
This resource is provided by the Great Britain Philatelic Society
Barred Numeral Cancellations of Ireland – http://www.gbps.org.uk/information/downloads/files/postal-markings/1844%20Irish%20Numerals%20Scarcity%20Ratings.pdf
This resource is provided by the Great Britain Philatelic Society
The Registration ‘Rotary Device’ – http://www.gbps.org.uk/information/downloads/files/postal-markings/The%20Registration%20Rotary%20Device%20-%20Maurice%20Buxton%20(2020).pdf
This resource is provided by the Great Britain Philatelic Society
Collecting Slogan Postmarks – 1917-1969 – http://www.gbps.org.uk/information/downloads/files/postal-markings/Vol.%201%20-%20Collecting%20Slogan%20Postmarks%20(1917-1969).pdf
This resource is provided by the Great Britain Philatelic Society
Postage Paid Franks and Cancellations of the Channel Islands – http://www.gbps.org.uk/information/downloads/files/postal-markings/Postage%20Paid%20Franks%20and%20Cancellations%20of%20the%20Channel%20Islands%20-%20Glenn%20H%20Morgan%20(1983).pdf
This resource is provided by the Great Britain Philatelic Society