Critical incidents and work diaries: The critical incident technique asks subject matter experts to identify critical aspects of behavior or performance in a particular job that led to success or failure. For example, the supervisor of an electric utility repairman might report that in a very time-pressing project, the repairman failed to check a blueprint and as a result cut a line, causing a massive power loss. In fact, this is what happened in Los Angeles in September 2005 when half the city lost power over a period of 12 hours. The second method, a work diary, asks workers and/or supervisors to keep a log of activities over a prescribed period of time. They may be asked to simply write down what they were doing at 15 minutes after the hour for each hour of the work day. Or, they may list everything they have done up to a break.