▁of ▁a ▁chip ▁log ▁in ▁a ▁specific ▁time . ▁ ▁De fin itions ▁ 1 ▁international ▁kn ot ▁= ▁ 1   na ut ical ▁mile ▁per ▁hour ▁( by ▁definition ), ▁ ▁( ex actly ), ▁ ▁( appro xim ately ), ▁ ▁( appro xim ately ), ▁ ▁( appro xim ately ) ▁ ▁( appro xim ately ). ▁ ▁The ▁length ▁of ▁the ▁intern ation ally ▁agreed ▁na ut ical ▁mile ▁is ▁. ▁The ▁US ▁adopted ▁the ▁international ▁definition ▁in ▁ 1 9 5 4 , ▁having ▁previously ▁used ▁the ▁US ▁na ut ical ▁mile ▁( ). ▁The ▁UK ▁adopted ▁the ▁international ▁na ut ical ▁mile ▁definition ▁in ▁ 1 9 7 0 , ▁having ▁previously ▁used ▁the ▁UK ▁Admir alty ▁na ut ical ▁mile ▁( ▁or ▁). ▁ ▁Us age ▁The ▁spe eds ▁of ▁vessels ▁relative ▁to ▁the ▁flu ids ▁in ▁which ▁they ▁travel ▁( bo at ▁spe eds ▁and ▁air ▁spe eds ) ▁are ▁measured ▁in ▁kn ots . ▁For ▁consist ency , ▁the ▁spe eds ▁of ▁navig ational ▁flu ids ▁( tid al ▁streams , ▁river ▁curr ents ▁and ▁wind ▁spe eds ) ▁are ▁also ▁measured ▁in ▁kn ots . ▁Thus , ▁speed ▁over ▁the ▁ground ▁( SO G ; ▁ground ▁speed ▁( GS ) ▁in ▁aircraft ) ▁and ▁rate ▁of ▁progress ▁towards ▁a ▁distant ▁point ▁(" vel ocity ▁made ▁good ", ▁VM G ) ▁are ▁also ▁given ▁in ▁kn ots . ▁ ▁Origin ▁ ▁Until ▁the ▁mid - 1 9 th ▁century , ▁vessel ▁speed ▁at