Another approach is to ask workers to keep a diary/log of what they do during the day, for every activity he or she engages in, the employee records the activity (along with the time) in a log.
(Daily listings made by workers of every activity in which they engage along with the time each activity takes). This can produce a very complete picture of the job. Especially when supplemented with subsequent interviews with the worker and the supervisor. The employee, of course, might try to exaggerate some activities and underplay others. However, the detailed, chronological nature of the log tends to meditate against this.
Some firms take a high-tech approach to diary/logs. They give employees pocket dictating machines and pagers. Then at random times during the day, they page the workers, who dictate what they are doing at that time. This approach can avoid one pitfall of the traditional diary/log method relying on workers to remember what they did hours earlier when they complete their logs at the end of the day.