Notes on verification

Corrected 2026-09-06 verification pass: original wording ('celestial navigation made it difficult for ships to keep track of their position') was backwards — celestial navigation was the tool, and it worked well for latitude. Per Britannica Longitude Measurements: latitude was determinable from the Sun's noon altitude or a star's meridian crossing, but longitude at sea required an accurate timekeeper, and no shipboard clock kept accurate time until John Harrison's marine chronometer. Primary source reassigned from Wikipedia 'Blown off course' stub (source_id=10) to Britannica Longitude Measurements (source_id=731). Also corroborated by Warwick CAGE (source_id=730), Smithsonian Time and Navigation (source_id=733), and Encyclopedia.com (source_id=1088). Cleared aggregator_dropped_primary_exists flag. [tier=silver indep_score=0.700 clusters=9 claim_tier=notable reviewed_by=verification_pass_2026_09_06]