Capturing data in this way had several clear advantages.
1. No additional employees were needed to serve as observers.
2. Operators Know more accurately than an observer can exactly what they are doing at the instant of the sampling signal. An observer might have to ask what the operator was doing.
3. Making three or four sampling entries per shift is enormously easier for operators than keeping accurate, detailed diaries.
4. A genuinely random time sampling study is inherently more accurate than a diary study.