The "Dodo-Postcards" watermark is NOT on the actual card – it is an online watermark only.
24 hour gate clock. Old Royal Observatory. National Maritime Museum. Her Majestys Stationery Office by E. Baylis. 1976
24 hour gate clock. Old Royal Observatory. National Maritime Museum. Card No. 252. Albion Printers
Greenwich Planetarium. Old Royal Observatory. National Maritime Museum. Greenwich. Card No. 231. W. S. Cowell
The Time Ball Signal. Old Royal Observatory. National Maritime Museum. The Artisan Press
Greenwich. The Old Royal Observatory. National Maritime Museum. Larkfield Printing
The Time Ball Signal. Old Royal Observatory. National Maritime Museum
Greenwich Mean Time. 24 hour public clock at Old Royal Observatory. National Maritime Museum. Larkfield Printing Company. Yorkshire. ENT 4
