Arbitrary measures of efficiency unsettle the dichotomy between engineering efficiency and efficiency in more popular forms: this dichotomy runs through the literature on the progressive era USA. Arbitrary efficiency standards were developed late in the progressive era for use in cases where ideal or theoretical efficiency could not be calculated. Arbitrary standards mediated between technical efficiency and efficiency's other forms, and illustrate important similarities between them. Examples of technical efficiency from Engineering Magazine, a prominent engineering journal, and of personal efficiency from the Independent, a prominent general interest journal of reform, reveal a common emphasis on efficiency as a tool of balance. In both, efficiency was a tool to help guarantee regularity, stability, and reliability, and used similar techniques of control, including continual surveillance and adjustment and deference to outside authority. Arbitrary measures of efficiency crossed the boundaries between the technical and personal, and underscore a shared foundation in their reliance on expertise.Many of the young women in the Sayles Bleachery became friends after they were observed at work in 1909 by Henry Gantt, efficiency consultant and mechanical engineer, disciple of Frederick Winslow Taylor (with whom he later broke), and graduate of Johns Hopkins University and the Stevens Institute of Technology. The women formed a club, began to socialize with each other after work, and even had matching pins made to symbolize their status as members of the efficiency study. Gantt created graphs of their efficiency (see an example in Fig. 1); black was efficient, red (here, gray) was not. The graph was a predecessor of the Gantt chart, a tool of engineering management still in wide use. It illustrates a combination of technical and personal efficiencies, and dates from the progressive era, when concern for efficiency was at its height, for efficiency in industry, in government and Social Studies of Science 38/3 (June 2008) 323-349