▁using ▁Sm o ots ▁to ▁measure ▁the ▁locations ▁of ▁acc idents ▁and ▁inc idents ▁on ▁the ▁bridge . ▁When ▁the ▁original ▁mark ings ▁were ▁removed ▁or ▁covered ▁over ▁during ▁bridge ▁maintenance , ▁the ▁police ▁had ▁to ▁request ▁that ▁someone ▁re apply ▁the ▁Sm oot ▁scale ▁mark ings . ▁During ▁a ▁major ▁bridge ▁re build , ▁the ▁concrete ▁side walk ▁was ▁perman ently ▁divided ▁into ▁segments ▁one ▁Sm oot ▁in ▁length , ▁as ▁opposed ▁to ▁the ▁regular ▁division ▁of ▁six ▁feet . ▁ ▁W iff le ▁A ▁W iff le , ▁also ▁referred ▁to ▁as ▁a ▁W AM ▁for ▁W iff le ▁( ball ) ▁Ass isted ▁Me asure ment , ▁is ▁equal ▁to ▁a ▁sphere ▁ 8 9 ▁mill im eters ▁( 3 . 5 ▁inches ) ▁in ▁diameter ▁– ▁the ▁size ▁of ▁a ▁W iff le ▁ball , ▁a ▁per for ated , ▁light - weight ▁pl astic ▁ball ▁frequently ▁used ▁by ▁marine ▁bi olog ists ▁as ▁a ▁size ▁reference ▁in ▁photos ▁to ▁measure ▁cor als ▁and ▁other ▁objects . ▁The ▁spher ical ▁shape ▁makes ▁it ▁om n id irection al ▁and ▁perfect ▁for ▁taking ▁a ▁speed y ▁measurement , ▁and ▁the ▁open ▁design ▁also ▁allows ▁it ▁to ▁avoid ▁being ▁cr ushed ▁by ▁water ▁pressure . ▁W iff le ▁balls ▁are ▁a ▁much ▁che aper ▁alternative ▁to ▁using ▁two ▁reference ▁las ers , ▁which ▁often ▁pass ▁straight ▁through ▁g aps ▁in ▁thin ▁cor als . ▁ ▁A ▁scient ist ▁on ▁the ▁research ▁vessel ▁ ▁is ▁cred ited ▁with ▁pione ering ▁the ▁technique