"Detesters, Phasers and Dean Drives", a 1976 article by Davis, reported his tests with Stine, an engineer who built devices to test that aspect of the hypothesis. Stine said they were able to reliably create and reproduce a 3-degree phase angle in a linear system, which was not possible according to ordinary physics. But then they failed to reproduce the effect in a pendulum system, using a rocket-powered ballistic pendulum. The pendulum test would have proved beyond doubt that the Drive worked, but Dean refused to subject the original Dean Drive to a pendulum test. Campbell reported that he had seen the Drive subjected to a pendulum test, but Davis and Stine suspect that he only reported what Dean had told him and had never seen the actual test. Davis says the question can't be settled until the pendulum test is made. Their research was terminated in 1965 when the national economy took a downturn, and was never resumed. The 1976 article was an attempt to get research restarted, but apparently failed.