Computer simulations are increasingly used to study the development, adoption, and evolution of technologies. However, existing models suffer from various drawbacks that may not be easily corrected, among them lack of internal structure in technologies, static environments and practical difficulties of introducing rational or semi-rational search for solutions. This paper discusses the theoretical background and rationale for an improved model, the Adder, and sketches out the model's main features. As an example of the model?s flexibility, we use it to provide insight into why uncertainty about performance of technologies and user needs may be an essential component in the evolution of technology.