Vambola Hurt, Elmar Ojaste. Eesti / Estonia: philately & postal history handbook-catalogue / Estland: Philatelie & Postgeschichte Handbuch-katalog
http://viki.filateelia.ee/index.php/Vam ... ch-katalog
11 Mute cancellations in Estonia 1914 / Stumme Stempel in Estland 1914
https://viki.filateelia.ee/index.php/11 ... tland_1914