Thomas Morel’s Underground Mathematics reconstructs subterranean geometry, or Markscheidekunst, as a neglected form of practical mathematics developed in the mining regions of the Holy Roman Empire. Morel presents mine surveying as a craft culture in which measurement, legal procedure, manuscript practice, map-making, and administrative record-keeping jointly made the underground knowable. This review reads the book through technical language, representation, and trust. Its central claim is that hidden subterranean space became measurable, legible, and usable through situated procedures and records. Surveying rituals, handwritten manuals, maps, and administrative documents did not merely record technical practice, they helped define what counted as reliable knowledge within mining communities. For readers concerned with technology and language, the book is valuable because it shows how authority emerged through the interplay of vocabularies, instruments, numerical measurement, visual forms, and legal-administrative procedures. The book is therefore important for historians of mathematics, mining, and craft culture, as well as for readers interested in how technical practices generate legibility, authority, and trust. Although Morel could have developed more explicit reflections on technical language, visual mediation, and the geographical boundaries of subterranean geometry, Underground Mathematics remains a compelling study of how measurement, inscription, and visualization transformed hidden subterranean spaces into objects of knowledge, judgment, and administration.