The precis of Project Ernestine or an overview of a validation of GOMS

INTRODUCTION Project Ernestine served a pragmatic as well as a scientific goal: to compare the worktimes of telephone company toll and assistance operators on two different workstations, and to test the validity of GOMSl models for predicting and explaining real-world performance. Contrary to expectations, GOMS predicted and the data confirmed, that performance with the proposed workstation was slower than with the current one, Pragmaticly, this increase in performance time translates into a cost of 2. 4 million dollars a year to NYNEX. Scientificly, the GOMS models predicted performance with exceptional accuracy.