An implementation of interprocedural constant propagation must model the transmission of values through each procedure. In the framework proposed by Callahan, Cooper, Kennedy, and Torczon in 1986, this intraprocedural propagation is modeled with a jump function. While Callahan et al. propose several kinds of jump functions, they give no data to help choose between them. This paper reports on a comparative study of jump function implementations. It shows that different jump functions produce different numbers of useful constants; it suggests a particular function, called the pass-through parameter jump function, as the most cost-effective in practice.