▁sea ▁was ▁measured ▁using ▁a ▁chip ▁log . ▁This ▁consisted ▁of ▁a ▁wooden ▁panel , ▁attached ▁by ▁line ▁to ▁a ▁re el , ▁and ▁weight ed ▁on ▁one ▁edge ▁to ▁float ▁per pend icular ly ▁to ▁the ▁water ▁surface ▁and ▁thus ▁present ▁substantial ▁resistance ▁to ▁the ▁water ▁moving ▁around ▁it . ▁The ▁chip ▁log ▁was ▁cast ▁over ▁the ▁stern ▁of ▁the ▁moving ▁vessel ▁and ▁the ▁line ▁allowed ▁to ▁pay ▁out . ▁K not s ▁placed ▁at ▁a ▁distance ▁of ▁ 4 7   fe et ▁ 3   in ches ▁( 1 4 . 4 0 1 8   m ) ▁from ▁each ▁other , ▁passed ▁through ▁a ▁sail or ' s ▁fingers , ▁while ▁another ▁sail or ▁used ▁a ▁ 3 0 - second ▁sand - glass ▁( 2 8 - second ▁sand - glass ▁is ▁the ▁currently ▁accepted ▁timing ) ▁to ▁time ▁the ▁operation . ▁The ▁kn ot ▁count ▁would ▁be ▁reported ▁and ▁used ▁in ▁the ▁sail ing ▁master ' s ▁dead ▁reck oning ▁and ▁navigation . ▁This ▁method ▁gives ▁a ▁value ▁for ▁the ▁kn ot ▁of ▁ 2 0 . 2 5   in / s , ▁or ▁ 1 . 8 5 1 6 6 ▁km / h . ▁The ▁difference ▁from ▁the ▁modern ▁definition ▁is ▁less ▁than ▁ 0 . 0 2 %. ▁ ▁Der iv ation ▁of ▁kn ots ▁spacing : ▁ ▁, ▁so ▁in ▁ ▁seconds ▁that ▁is ▁ ▁metres ▁per ▁kn ot . ▁ ▁Modern ▁use ▁ ▁Although ▁the ▁unit ▁kn ot ▁does ▁not ▁fit