We set up a study on 60 relatively healthy patients, undergoing various kind of surgery in general anaesthesia. The study is approved by the Regional Committee of Ethics in Medicine, Health Region East, and all patients give written informed consent. Both monitors (BIS and CSM) are applied to the patients, but only information from BIS is available for the anaesthetist throughout surgery. Information from the two monitors and from the routine monitoring equipment as well as from the actual delivery of anaesthetics is sampled online into a designed data program (Rugloop, Demed, Belgium).