CHASM (CHerenkov Air Shower Model) is a python package which leverages the universality of charged particles in an extensive air shower to produce a deterministic prediction of the Cherenkov light signal for a given shower profile and geometry. At sampled points throughout the domain of all shower development stages and altitudes, the angular and yield distributions of Cherenkov light have been calculated at an array of distances from a shower axis. Chasm accesses and interpolates between these distributions at runtime to produce the aggregate signal from the whole shower at user defined telescope locations. This paper gives a detailed description of the methods used to compute the Cherenkov distribution tables from universal charged particle energy and angular distributions. It also describes the workflow of CHASM itself, how a shower and axis is constructed, and how a user can customize the simulation. Finally, this paper describes how to install CHASM both from source code on GitHub and using pip (python's built in package manager) and how to use it.