Literature, Sweden. Handbooks. "Sveriges frankotecken 1855–1905" (SFF) (worn cover), "Handbok över Sveriges frankotecken 1855–1946" (SFF), "Den gula treskillingen" (Sven Åhman) (numbered edition, No. 43), "Svenska Postgirot 1925–1949" (Karl Wilhelmsson). All are used. (4).