The psychologists David Marks and Richard Kammann attempted to replicate Russell Targ and Harold Puthoff’s remote viewing experiments that were carried out in the 1970s at the Stanford Research Institute. In a series of 35 studies, they were unable to replicate the results, motivating them to investigate the procedure of the original experiments. Marks and Kammann discovered that the notes given to the judges in Targ and Puthoff's experiments contained clues as to the order in which they were carried out, such as referring to yesterday's two targets, or they had the date of the session written at the top of the page. They concluded that these clues were the reason for the experiment's high hit rates. Marks was able to achieve 100 per cent accuracy without visiting any of the sites himself but by using cues. James Randi wrote controlled tests in collaboration with several other researchers, eliminating several sources of cuing and extraneous evidence present in the original tests; Randi's controlled tests produced negative results. Students were also able to solve Puthoff and Targ's locations from the cues that had inadvertently been included in the transcripts.