Which of the following is the most common method used to know depth of anaesthesia

BIS- Bispectral index * BIS monitoring was first introduced for clinical use in 1996. It was approved by FDA as a technique of monitoring depth of anaesthesia and reducing the incidence of intraoperative awareness during General anaesthesia in 2004. * 100 - Awake * 80 - light / moderate sedation * 60 - General anaesthesia * 40 - Deep hypnotic state * 20 - burst suppression * 0 - isoelectric EEG Ref:- Understanding Anesthetic Equipment and Procedures - Baheti & Laheri Pg num:- 304,305