The so-called IL pavilion in Stuttgart, constructed by Frei Otto and the Institute for Lightweight Structures (IL) served itself as an experimental building for testing the execution of a new type of cable net construction. At this 1:1 mock-up various manufacturing techniques and measuring methods were tested, additionally to model tests on physical models. These models were necessary, because at that time no adequate calculation methods were available to design the complex geometries of such wide-span cable net constructions. In this paper, the authors clarify the way the model was produced, the development of the measurement methods and the impact of model testing for the execution of the innovative construction of the German pavilion for the World's Fair in Montréal in 1967. The physical model, which is one of the few surviving measurement models from this period, was digitally rebuilt with state of the arts methods in the context of the DFG research project “last witnesses”. The data extracted from the physical model was compared with a model generated from the original cut stencils. Overall, the numbers match fairly well, nevertheless there are some outliers due to the changed numbers of elements, which have a deviation of more than 40%. The data extracted from the digital twin will further be used to evaluate changed boundary conditions, increased snow loads or wind effects for the building itself and to record the actual state of the model for future preservation measures.