The Bistromathic Drive is a fictional type of starship propulsion system in Douglas Adams' Hitchhiker's Guide to the Galaxy. It is used in Slartibartfast's craft Starship Bistromath and works by exploiting the irrational mathematics used by groups of people in dividing up restaurant bills. Life, the Universe and Everything describes bistromathics as follows: "Bistromathics itself is simply a revolutionary new way of understanding the behaviour of numbers. Just as Einstein observed that space was not an absolute but depended on the observer's movement in time, so it is now realized that numbers are not absolute, but depend on the observer's movement in restaurants."