In the article “New York Rises with Concrete” (June 2005), there was a discussion of a self-rising gang form system used to construct the reinforced concrete core at 7 World Trade Center. We neglected to mention that the formwork solution was developed by PERI exclusively for this project. What makes this formwork unique is that the contractor erected the structural steel first, then came back and constructed the core encasing the steel columns and beams. Each typical 13-foot 6-inch lift of the core had 14,900 square feet of formed surface area and was constructed at a rate of one floor every two days.