In 1952, another person named A.S.Douglas was passing his PhD degree at the University of Cambridge (United Kindgom). At that time, the university had an EDSAC vaccuum-tube computer, which used a cathode ray tube to display the contents of one of the 32 mercury delay lines (which stored the programs and data). The display was organized as a matrix of 35 by 16 dots, hence a 35x16 pixel display. A.S. Douglas wrote his thesis on the Human-Computer interraction, and illustrated it with a graphic Tic-Tac-Toe game displayed on a cathode ray tube. This is the earliest graphical computer game known to exist. The game was played against the machine, which used special algorithms to win whenever possible. This game can be played nowadays using the EDSAC simulator, which includes a copy of the original game.