1847 cover bearing Haroldswick Island of Unst, Shetland Islands local handstamp

1847 stampless entire wrapper addressed to Edinburgh and rated at "1" in red manuscript on front together with a Lerwick datestamp for MR 13 1847 and bearing on reverse the Haroldswick local handstamp in black ink. Harolswick is Britain's most Northerly Post Office. A very scarce cover. Bov#431