The working time of reference librarians was sampled using random alarm devices and a structured checklist of mutually exclusive categories of reference questions. An average wage rate was applied to the unit time reciprocals derived from the resulting percentages. Wage costs for directional questions averaged $1.98; extended reference queries, $4.57. Random time sampling with self-observation gives acceptable reliability at low cost, minimal interference with service operations, and minimal distortion of collected data due to the collection process. It can be carried out by library managers themselves.