This article takes a single genre of the Persian Gulf pearl dive—the chau manual, used to determine the weight-based value of a pearl—and draws on it to think about circulation and commodification in the Indian Ocean world. In reading the chau manual, as well as other writings, it highlights the active processes by which economic actors in the region thought about, and indeed produced, capitalism at sea. As technologies—as means of doing—chau manuals allowed pearl merchants to move from the specificities and idiosyncrasies of nature to the abstractions of the market. More generally, texts like these formed part of the infrastructure through which circulation took place in the maritime marketplace. By thinking through these marketplace genres, we can gain a more textured sense of the processes of knowing, measuring, abstracting, and circulating that underpinned the maritime—a process of active economic thinking that went into the making of global capitalism in a corner of the Indian Ocean world.