Aco, along with PD, CLF and PCU are all down sharply today. Using Reuters free charting service to chart all four on the same screen, it is obvious that all four have moved sharply in the same direction at the same time for more than a year. They are all identified by Reuters as being in the construction sector and also in the building materials industry of that sector. They seem entrained together. Perhaps this is the sector that hedge funds are using to sell short while buying undervalued large caps. PCU is said to be 75% owned by Groupo Mexico. Perhaps it is easier to short stocks with a relatively small float. ACO is presently close to and following a decling lower band on the Bollinger chart.