This is Bligh's spare(?) needle for use in a prismatic hand bearing compass.
Unrecorded. The hitherto known means and method of Bligh's navigation of the Bounty's launch were recorded by John Back in his introduction to his transcription and facsimile of Bligh's 'Rough account...', The Bligh Notebook, Melbourne, 1987: 'there is certainly no mystery about the methods employed, as the notebook, with its daily calculations, proves. It was a simple case of rhumb line sailing, with plane and mid-latitude problems worked by traverse-tables in the normal manner. The information needed for these daily calculations of the launch's position were provided by a Ramsden ten-inch sextant, of established accuracy, a quadrant of adequate precision, and Adams compass taken from the BOUNTY's binnacle and a log-line, made up in the launch a few days after the voyage began and for the use of which the men had learnt to count accurately in seconds. To provide mathmatical, astronomical and geographical information there were in the launch two well-known standard printed books, the more important of which probably that by Hamilton Moore, a comprehensive manual on navigation and a leading publication in its field, providing by itself all the necessary information.' (op. cit., pp.29-30).