Refinement techniques play a major role to build a complex system incrementally. Refinement is supported by several modelling techniques in the area of system designing. These modelling techniques focus on notations that are either text or graphical. This article focuses on refinement chart (RC) that is based on graphical notations. The refinement chart is a graphical representation of a complex system using layering approach, where functional blocks are di- vided into multiple simpler blocks in a new refinement level, without changing the original behaviour of the system. The main contribution of this article is to provide the formal semantical description of the refinement chart. The refinement chart offers a clear view of assistance in "system" integration that assists to model the complex critical systems. Moreover, it also sketches a clear view of different operating modes and their associated components. To realise the effectiveness of this approach, we apply this refinement based graphical modelling technique to model an industrial case study: Adaptive Cruise Control (ACC).