GKS 1812 is a broadly encyclopedic work consisting of four texts (identifiable by distinct scribal hands) composed during the 12th through 14th centuries. Among the various works included in the manuscript are two of a specifically mathematical nature: an Old Norse prose translation of the Carmen Algorismo, a Latin text on the use of the Indo-Arabic numeration system, and a one page exposition of some geometric relationships between a circle and an inscribed equilateral triangle. The Old Norse Algorismus is unique among such works for containing a final section on a supposed connection between a geometric progression between cubes and the four elements, a neoplatonic formulation that has roots in the Timaeus. Beyond providing transcripts, translations, and expositions of the methods of these two texts, this volume investigates the neoplatonic background of the final section and looks at the philosophical setting of the texts from a modern perspective.