In 2006, Christensen commented on the four automated depots introduced by Davis, saying "not a single day went by without one, if not all of them, breaking down... The systems were flawed. They have to stop for four hours every day for maintenance. But because they were constantly breaking down you would be playing catch up. It was a vicious circle." Christensen said a fundamental mistake was to build four such depots at once, rather than building one which could be thoroughly tested before progressing with the others.