This study was designed to micro-analyze the role of the design of interactive diagrams in learning-teaching the concept of the indefinite integral. The presented case study focuses on the engagement of one pair of 17-year-old students with an interactive diagram for graphically learning-teaching the indefinite integral concept. The authors performed three rounds of analysis to detect the mathematical elements involved in finding connections between the function graphs and the antiderivative function graphs and to identify how the design features of the interactive diagram functioned in the students' engagement processes. The data analysis identified how the pedagogical functions designed in the interactive calculus diagram were reflected in the students' learning-teaching processes with the diagram.