▁the ▁t issue ▁model ▁and ▁recent ▁div ing ▁history ▁of ▁the ▁user ). ▁ ▁Res id ual ▁in ert ▁gas ▁can ▁be ▁computed ▁for ▁all ▁mode led ▁t issues , ▁but ▁repet itive ▁group ▁design ations ▁in ▁decom pression ▁tables ▁are ▁generally ▁based ▁on ▁only ▁the ▁one ▁t issue , ▁considered ▁by ▁the ▁table ▁design ers ▁to ▁be ▁the ▁most ▁limit ing ▁t issue ▁for ▁likely ▁applications . ▁In ▁the ▁case ▁of ▁the ▁US ▁Navy ▁Air ▁T ables ▁( 1 9 5 6 ) ▁this ▁is ▁the ▁ 1 2 0 ▁minute ▁t issue , ▁while ▁the ▁Bü hl mann ▁tables ▁use ▁the ▁ 8 0 ▁minute ▁t issue . ▁ ▁D iving ▁at ▁alt itude ▁▁ ▁The ▁atmos pher ic ▁pressure ▁decre ases ▁with ▁alt itude , ▁and ▁this ▁has ▁an ▁effect ▁on ▁the ▁absolute ▁pressure ▁of ▁the ▁div ing ▁environment . ▁The ▁most ▁important ▁effect ▁is ▁that ▁the ▁diver ▁must ▁decom press ▁to ▁a ▁lower ▁surface ▁pressure , ▁and ▁this ▁requires ▁longer ▁decom pression ▁for ▁the ▁same ▁d ive ▁profile . ▁A ▁second ▁effect ▁is ▁that ▁a ▁diver ▁asc ending ▁to ▁alt itude , ▁will ▁be ▁decom press ing ▁en ▁route , ▁and ▁will ▁have ▁resid ual ▁nit ro gen ▁until ▁all ▁t issues ▁have ▁equ il ibr ated ▁to ▁the ▁local ▁press ures . ▁This ▁means ▁that ▁the ▁diver ▁should ▁consider ▁any ▁d ive ▁done ▁before ▁equ il ibration ▁as ▁a ▁repet itive ▁d ive , ▁even ▁if ▁it ▁is ▁the ▁first ▁d ive ▁in ▁several ▁days . ▁The ▁US