For the initial stages of architectural training one of the strategies traditionally used is to study design cases. This exercise can help in the comprehension of implicit geometries and design processes. The use of the golden ratio, for example, is recurrent in the history of architecture. However, adequate instruments are necessary for this kind of statement. This paper demonstrates the use of Augmented Reality with this goal: virtual elements are viewed overlaying the architecture or its representation, configuring a “digital proportion measurer”. The comprehension of known architectural practices assists in structuring methods and constructing repertoires for architectural design.