7 0 s ), ▁the ▁custom ary ▁units ▁have ▁a ▁strong ▁hold ▁due ▁to ▁the ▁vast ▁industrial ▁infrastr ucture ▁and ▁commercial ▁development . ▁ ▁While ▁imperial ▁and ▁US ▁custom ary ▁systems ▁are ▁closely ▁related , ▁there ▁are ▁a ▁number ▁of ▁differences ▁between ▁them . ▁Units ▁of ▁length ▁and ▁area ▁( the ▁in ch , ▁foot , ▁yard , ▁mile ▁etc .) ▁have ▁been ▁identical ▁since ▁the ▁ad option ▁of ▁the ▁International ▁Y ard ▁and ▁P ound ▁Ag re ement , ▁however ▁America ▁and , ▁formerly , ▁India ▁retained ▁older ▁definit ▁for ▁surve ying ▁purposes . ▁This ▁gave ▁rise ▁to ▁the ▁US ▁survey ▁foot ▁for ▁instance . ▁The ▁A voir du pois ▁units ▁of ▁mass ▁and ▁weight ▁differ ▁for ▁units ▁larger ▁than ▁a ▁p ound ▁( lb ). ▁The ▁imperial ▁system ▁uses ▁a ▁stone ▁of ▁ 1 4   lb , ▁a ▁long ▁hundred weight ▁of ▁ 1 1 2   lb ▁and ▁a ▁long ▁ton ▁of ▁ 2 2 4 0   lb . ▁The ▁stone ▁is ▁not ▁used ▁in ▁the ▁US ▁and ▁the ▁hundred we ights ▁and ▁tons ▁are ▁short : ▁ 1 0 0   lb ▁and ▁ 2 0 0 0   lb ▁respectively . ▁ ▁Where ▁these ▁systems ▁most ▁not ably ▁differ ▁is ▁in ▁their ▁units ▁of ▁volume . ▁A ▁US ▁fluid ▁ ounce ▁( fl   oz ), ▁about ▁ 2 9 . 6 ▁mill il it res ▁( ml ), ▁is ▁slightly ▁larger ▁than ▁the ▁imperial ▁fluid ▁ ounce ▁( about ▁ 2 8 . 4  