rol abe , ▁a ▁method ▁to ▁correct ▁for ▁the ▁alt itude ▁of ▁Pol aris ▁and ▁rud iment ary ▁na ut ical ▁charts ▁were ▁all ▁the ▁tools ▁available ▁to ▁a ▁navig ator ▁at ▁the ▁time ▁of ▁Christopher ▁Columb us . ▁ ▁In ▁his ▁notes ▁on ▁P to le my ' s ▁ge ography , ▁Johannes ▁Werner ▁of ▁N uren berg ▁wrote ▁in ▁ 1 5 1 4 ▁that ▁the ▁cross - st aff ▁was ▁a ▁very ▁ancient ▁instrument , ▁but ▁was ▁only ▁beginning ▁to ▁be ▁used ▁on ▁ships . ▁ ▁Prior ▁to ▁ 1 5 7 7 , ▁no ▁method ▁of ▁jud ging ▁the ▁ship ' s ▁speed ▁was ▁mentioned ▁that ▁was ▁more ▁advanced ▁than ▁obser ving ▁the ▁size ▁of ▁the ▁vessel ' s ▁bow ▁wave ▁or ▁the ▁passage ▁of ▁sea ▁fo am ▁or ▁various ▁floating ▁objects . ▁ ▁In ▁ 1 5 7 7 , ▁a ▁more ▁advanced ▁technique ▁was ▁mentioned : ▁the ▁chip ▁log . ▁ ▁In ▁ 1 5 7 8 , ▁a ▁pat ent ▁was ▁registered ▁for ▁a ▁device ▁that ▁would ▁judge ▁the ▁ship ' s ▁speed ▁by ▁counting ▁the ▁revolution s ▁of ▁a ▁wheel ▁mounted ▁below ▁the ▁ship ' s ▁water line . ▁ ▁Acc ur ate ▁time - keep ing ▁is ▁necessary ▁for ▁the ▁determ ination ▁of ▁longitude . ▁ ▁As ▁early ▁as ▁ 1 5 3 0 , ▁prec urs ors ▁to ▁modern ▁techniques ▁were ▁being ▁expl ored . ▁ ▁However , ▁the ▁most ▁accurate ▁clock s ▁available ▁to ▁these ▁early ▁navig ators ▁were ▁water ▁clock s