 
 <prompt> Chronometers fit measure time, e dey useful for sailing, but e no fit determine which measurement dey accurate? Given di last question, write one context wey contain di answer. E fit be 1 - 20 sentences. Context: <response>: ```Captain John Byron waka pass through di islands of Tuvalu for 1764 during im journey around di world as captain of di Dolphin (1751). Byron draw map of di atolls as Lagoon Islands. Keith S. Chambers and Doug Munro (1980) identify Niutao as di island wey Francisco Mourelle de la Rúa sail pass on 5 May 1781, so e solve wetin Europeans bin dey call The Mystery of Gran Cocal. Mourelle's map and journal name di island El Gran Cocal ('The Great Coconut Plantation'); but, di latitude and longitude bin dey uncertain. Longitude fit only dey estimated roughly as accurate chronometers no dey available until di late 18th century.``` 