Human factors engineering research into human-computer interaction (HCI) needs means to easily and objectively study HCI. The Instrumented Interface Construction (IICON) Evaluator, and its associated IICON Data Taps, provide such means. Any X Window system user interface built using development tools for which appropriate IICON Data Taps exist (e.g., IICON Data Taps/TAE+5.2) can be automatically instrumented. Instrumented interfaces can then be used by subjects, recording a complete transcript of user actions. Once an operator's session has been recorded, it can be replayed on-screen as needed for further observation and analysis. These capabilities are extremely helpful for developing cognitive task models (i.e., user models) for analytic purposes, or for construction of Intelligent Agents to be embedded in the operator's computer-based workstation. Furthermore, with a complete objective record of all operator actions, IICON Evaluator supports a wide variety of research investigations of HCI.