Audemars Piguet. A very rare and unusual octagonal 18K white gold keyless lever pendant watch

Audemars Piguet. A very rare and unusual octagonal 18K white gold keyless lever pendant watch
Signed Audemars Piguet, Royal Oak model, ref. 5691BC, movement no. 227'409, case no. B49733, circa 1981
Cal. 5020 mechanical movement, black textured dial, baton numerals, octagonal case with screwed bezel, winding crown at 12 o'clock, case back engraved 'Royal Oak', snap on back, case, dial and movement signed
44 mm. diam.