This study deals with the building of a specific set of economic valuations throughout the work of French telephone engineers between 1880 and 1938. In so doing, it contributes to our understanding of the complex interplay between economization and valuation. Tracing the changing practices that facilitated a shift from valuation aimed at minimizing force losses to valuation aimed at assessing and enhancing subjective utility, economizing is considered as an epistemic process, through which managers, engineers and workers are exploring, representing and transforming the world. From saving work and minimizing losses to creating value, engineers went from evaluating (telling what is worth, within an economy of force, optimizing the ratio of losses over total work) to valorizing (framing value as possibly produced and not only saved, the production of utility). This new concern for valorization points to the development of new ideas on what could create economic value. In this process, the very acts of measuring, optimizing and calculating, appeared as both “subversive” and “subverted”.