engers ▁to ▁carry ▁certific ates ▁and ▁checks . ▁The ▁mechan isms ▁bro k ers ▁used ▁to ▁transfer ▁se cur ities ▁and ▁keep ▁records ▁re lied ▁heavily ▁on ▁pen ▁and ▁paper . ▁The ▁exchange ▁of ▁physical ▁stock ▁certific ates ▁was ▁difficult , ▁in efficient , ▁and ▁increasing ly ▁expensive . ▁ ▁In ▁the ▁late ▁ 1 9 6 0 s , ▁with ▁an ▁un pre ced ented ▁sur ge ▁in ▁trad ing ▁leading ▁to ▁volumes ▁of ▁nearly ▁ 1 5 ▁million ▁shares ▁a ▁day ▁on ▁the ▁NY SE ▁in ▁April ▁ 1 9 6 8 ▁( as ▁opposed ▁to ▁ 5 ▁million ▁a ▁day ▁just ▁three ▁years ▁earlier , ▁which ▁at ▁the ▁time ▁had ▁been ▁considered ▁over wh el ming ), ▁the ▁paper work ▁bur den ▁became ▁enorm ous . ▁ ▁Stock ▁certific ates ▁were ▁left ▁for ▁weeks ▁p iled ▁ha ph az ard ly ▁on ▁any ▁level ▁surface , ▁including ▁fil ing ▁cabin ets ▁and ▁tables . ▁Sto cks ▁were ▁ma iled ▁to ▁wrong ▁addresses , ▁or ▁not ▁ma iled ▁at ▁all . ▁O vert ime ▁and ▁night ▁work ▁became ▁mand atory . ▁ ▁Turn over ▁was ▁ 6 0 % ▁a ▁year . ▁ ▁To ▁deal ▁with ▁this ▁large ▁volume , ▁which ▁was ▁over wh el ming ▁bro ker age ▁fir ms , ▁the ▁stock ▁ex changes ▁were ▁forced ▁to ▁close ▁every ▁week ▁( they ▁chose ▁every ▁Wed nes day ), ▁and ▁trad ing ▁hours ▁were ▁short ened ▁on ▁other ▁days ▁of ▁the ▁week . ▁ ▁Two ▁things ▁solved ▁the ▁crisis :