This research examined the impact of Computerized Performance Monitoring and Control Systems (CPMCSs) on service workers and their perceptions of work. Drawing on a thermostat model of control systems, the work built a causal model of CPMCS impact. The model demonstrated how four monitor design dimensions (tasks measured, frequency of measurement, object of monitoring, and recipient of the monitor data) affected the importance employees placed on production and service. Other constructs in the model included employees' acceptance of quantitative measures, computer appropriateness, computer accuracy, and employer's production and service messages. Using a holdback sample, an initial and revised model were tested on responses from 1,498 workers in 51 Canadian service sector organizations. Both versions of the model exhibited good explanatory power. The research led to three important conclusions. First, monitoring may not increase production. Even if it does, it need not reduce the importance of service. Second, studying monitors as multidimensional systems demonstrates that various monitor features can be altered to change the impact. Third, the credibility of the computer is a factor in the monitor's impact.