Textbook of Usability

Abstract. The Project Ernestine study of NYNEX telephone toll-and-assistance operators. A CPM-GOMS analysis correctly predicted that a new operator workstation (sold as faster and more ergonomic) would in fact be about 4 percent slower per call than the workstation it was replacing, because the redesigned workflow disrupted the tightly overlapped parallel activities that experienced operators had developed. The prediction was confirmed in a field trial and saved NYNEX tens of millions of dollars.