▁move ▁back ward ▁or ▁forward , ▁or ▁not ▁move , ▁depending ▁on ▁the ▁frequency ▁of ▁the ▁stro be - flash . ▁If ▁the ▁flash ▁occurs ▁equal ▁to ▁the ▁period ▁of ▁rotation ▁( or ▁an ▁even ▁multiple , ▁i . e . ▁ 2 * π * n / ω , ▁where ▁n ▁is ▁an ▁integer ▁and ▁ ω ▁the ▁angular ▁frequency ), ▁the ▁marked ▁point ▁will ▁appear ▁to ▁not ▁move . ▁Any ▁non - integer ▁flash ▁setting ▁will ▁make ▁the ▁mark ▁appear ▁to ▁move ▁forward ▁or ▁back ward , ▁e . g . ▁a ▁slight ▁increase ▁of ▁the ▁flash ▁frequency ▁will ▁make ▁the ▁point ▁appear ▁to ▁move ▁back ward . ▁ ▁A ▁common ▁use ▁of ▁a ▁stro be ▁flash ▁is ▁to ▁optimize ▁a ▁car ▁engine ' s ▁efficiency ▁at ▁a ▁certain ▁rot ational ▁period ▁by ▁direct ing ▁the ▁stro be - light ▁towards ▁a ▁mark ▁on ▁the ▁fly w heel ▁on ▁the ▁engine ' s ▁main ▁ax le . ▁The ▁stro be - light ▁tool ▁for ▁such ▁ign ition ▁timing ▁is ▁called ▁a ▁timing ▁light . ▁St ro be ▁light ing ▁has ▁also ▁been ▁used ▁to ▁see ▁the ▁movements ▁of ▁the ▁vocal ▁ch ords ▁in ▁slow ▁motion ▁during ▁speech , ▁a ▁procedure ▁known ▁as ▁video - st rob os copy . ▁ ▁Other ▁▁ ▁St ro be ▁lights ▁are ▁used ▁in ▁scientific ▁and ▁industrial ▁applications , ▁and ▁are ▁often ▁used ▁for ▁aircraft ▁anti - coll ision ▁light ing ▁both ▁on ▁aircraft ▁themselves ▁and ▁also ▁on ▁tall ▁station ary ▁objects , ▁such ▁as ▁television