This paper examines a 226 CE debate on li 曆 mathematical astronomy at the Cao-Wei (226–265) court as a case study in the role of orality and person-to-person exchange in the transmission of astronomical knowledge in early imperial China. The li- and mathematics-related manuscripts to have come down to us from the early imperial period often suffer from textual corruption, the form that this corruption takes being rooted in a culture of manuscript transmission by visual copying. Where numbers are involved, such corruption can significantly affect a text’s readability, reliability, and utility, and it is hardly a surprise, I argue, that actors speak of learning li by any way but reading. In 226 CE, two men showed up to a debate with different versions of Liu Hong’s 劉洪 (fl. 167–206 CE) Supernal Icon li (Qianxiang li 乾象曆), the one—the assistant director of the astronomical bureau—trying to best it, and the other—Liu Hong’s disciple—trying to defend it. Reconstructing the tortuous route by which Liu Hong’s astronomy made it into each man’s hands via a transmission network spanning the Three Kingdoms, I argue that this debacle, and its conclusion, are to be expected from the mode of oral and written transmission particular to astronomy in this age.