Australia 1982 60c Humpback Whale Trial Print UM

1982 60c Humpback Whale TRIAL / ESSAY PRINT with solid blue-green background (SG 841a / BW 930 E(1)). Superb UM example of this interesting stamp. Apparently a couple of the trial/essay printing sheets were issued in error thus giving rise to the SG catalogue listing. (cv£250). See additional image below.