In the course of the Moon books, however, Calculus leads a team of scientists and engineers working on a major rocket project, motivating him to adopt an ear trumpet, and later a hearing aid, and for the duration of the adventure he has near-perfect hearing. This made him a more serious character, even displaying leadership qualities that had not been shown before or since. However, after completing the journey to the Moon, Calculus discarded his hearing aid, forcing his friends to readjust to his hearing impairment (aside from one panel in The Castafiore Emerald, when Tintin is seen speaking to him through his ear-trumpet); this restored the humour surrounding him, though it could be that he finds his deafness useful since it enables him to focus on his work (something useful for The Calculus Affair, since he was referencing ultrasonic sound).