Bart Billings

• A Handbook of U. S. Postal Markings Impressed by Machines
• A handbook, US postal markings impressed by machines
• American Postal Machines Co. transfer of flag cancelation [sic] dies
• An Anthology of Machine Postal Markings
• Same year use of different flag cancellation dies
• Universal Stamping Machine Co. machines and postal markings (Machine Cancel Society specialized study)