In this paper we describe the development and initial testing of a tool for self-assessment of affect while interacting with computer systems: the Sensual Evaluation Instrument. We discuss our research approach within the context of existing affective and HCI theory, and describe stages of evolution of the tool, and initial testing of its effectiveness. Author Keywords Affective interaction, User-centered design, ambiguity, gesture-based interaction, embodiment. ACM Classification Keywords H.5.2 User interfaces