Calculus is partly modeled on inventor Auguste Piccard (1884–1962), Hergé stated in an interview with Numa Sadoul : "Calculus is a reduced scale Piccard, as the real chap was very tall. He had an interminable neck that sprouted from a collar that was much too large... I made Calculus a mini-Piccard, otherwise I would have had to enlarge the frames of the cartoon strip." The Swiss physics professor held a teaching appointment in Brussels when Hergé spotted his unmistakable figure in the street. In The Castafiore Emerald, Bianca Castafiore mentions that Calculus is "famous for his balloon ascensions", an ironic reference to Piccard.