The present thesis was part of a research effort aimed to promote interaction between the psychology of emotion and new developments in computing. The research was conducted within the context of a European project (PHYSTA: Principled Hybrid Systems, Theory and Applications). The main aim of the project was to create an emotion decoding system. Part of the project was to assemble a database with spontaneously occurring emotional episodes. To describe the perceived emotional content of these episodes, the project team developed a system called FEEL TRACE. This system was created in order to allow observers to track their perceptions of the emotional content of the audiovisual material in real time, leading to a 'trace' that shows variation over time. This tool is based on the dimensional approach to emotion, which has a long history in psychology and is represented by a two-dimensional space: the dimension of activation and the dimension of evaluation. A strong research tradition argues that emotion terms can be understood as referring to points in a space defined by those two axes. There are also strong suggestions that this space is circular. The circumference is defined by states that are at the limit of emotional intensity. These are equidistant from an emotionally neutral point, i.e. they define a circle, with alert neutrality at centre. This fundamental idea was gradually developed into a recording tool to present activation-evaluation space as a circle on a computer screen, and to have observers record their impression of emotional state by moving a cursor to the appropriate position in the space using a mouse. The development task was to ensure that users do so in a way that is consistent and whose meaning is reasonably clear. Pilot studies led to additions in the form of landmark words and colour coding.