Many studies into the process of producing and supervising dissertations exist, yet little research into the "product" of the Masters dissertation, or into how Masters supervision changes over time exist. Drawing on 62 semi-structured interviews with 31 Maths and Computer Science supervisors over a two-year period, this paper explores the Masters dissertation "product" and the temporal nature of its supervision. The paper argues that the UK Masters dissertation is, for supervisors, a "chameleon"; i.e. perfect for them to modify and adapt to any student within a diverse body in a short completion time. This, coupled with the evolving nature of supervision, means that although the Masters dissertation possesses a number of "core" characteristics, it is difficult to define; an "elusive chameleon". The paper argues that awareness of this will help counter misassumptions and inform supervision, and that further research into the Masters dissertation product will aid our understanding of supervision. (Contains 4 notes.)