Fig. 1. Through the verification methodology presented on this paper we were able to uncover a convergence problem within a publicly available marching-based isosurfacing code (top left) and fix it (top right). The problem causes the mesh normals to disagree with the known gradient field when refining the voxel size h (bottom row). The two graphs show the convergence of the normals before and after fixing the code.Abstract-Visual representations of isosurfaces are ubiquitous in the scientific and engineering literature. In this paper, we present techniques to assess the behavior of isosurface extraction codes. Where applicable, these techniques allow us to distinguish whether anomalies in isosurface features can be attributed to the underlying physical process or to artifacts from the extraction process. Such scientific scrutiny is at the heart of verifiable visualization -subjecting visualization algorithms to the same verification process that is used in other components of the scientific pipeline. More concretely, we derive formulas for the expected order of accuracy (or convergence rate) of several isosurface features, and compare them to experimentally observed results in the selected codes. This technique is practical: in two cases, it exposed actual problems in implementations. We provide the reader with the range of responses they can expect to encounter with isosurface techniques, both under "normal operating conditions" and also under adverse conditions. Armed with this information -the results of the verification process -practitioners can judiciously select the isosurface extraction technique appropriate for their problem of interest, and have confidence in its behavior.