Abstract: Space, Time and Architecture (SpTA) originated from Sigfried Giedion’s Norton Lectures for 1938–1939 at Harvard, renowned for their use of double-projection. Drawing on Giedion’s materials from the gta Archive at ETH Zurich, this paper reconstructs, for the first time, the slide sequences from the Lectures’ opening and closing sessions. By comparing with the illustrations in SpTA, it reveals shifts and flexibility in Giedion’s case selection within his classical-to-modern framework. It analyzes the 5 projection modes used in Giedion’s lantern slides and, building on Zeynep Ç. Alexander’s discussion on Wölfflin’s double slides pedagogy, argues that Giedion not only inherited his mentor’s method, but consciously advanced a Baroque-Modern approach of his own. This paper suggests that double-projection functioned at the time as an emerging but increasingly mature medium of both presentation and thought. Giedion’s technological innovation not only was a technic to promote modernism through his historical pedagogy, but also served as a key method in his thinking and construction of architectural history.