While the six women worked on ENIAC, they developed subroutines, nesting, and other fundamental programming techniques, and arguably invented the discipline of programming digital computers. Bartik and the other ENIAC female programmers learned to physically modify the machine, moving switches and rerouting cables, in order to program it. In addition to performing the original ballistic trajectories they were hired to compute, the six female programmers soon became operators on the Los Alamos nuclear calculations, and generally expanded the programming repertoire of the machine. Bartik's programming partner on the important trajectory program for the military that would prove that the ENIAC worked to specification was Betty Holberton known at the time as Betty Snyder. Bartik and Holberton's program was chosen to introduce the ENIAC to the public and larger scientific community. That demonstration occurred on February 15, 1946 and was a tremendous success. The ENIAC proved that it operated faster than the Mark I, a well known electromechanical machine at Harvard, and also showed that the work that would take a "human computer" 40 hours to complete could be done in 20 seconds.