Resource-bounded measure is a generalization of classical Lebesgue measure that is useful in computational complexity. The central parameter of resource-bounded measure is the resource bound Δ, which is a class of functions. Most applications of resource-bounded measure use only the "measure-zero/measure-one fragment" of the theory. For this fragment, Δ can be taken to be a class of type-one functions. However, in the full theory of resource-bounded measurability and measure, the resource bound Δ also contains type-two functionals. To date, both the full theory and its zero-one fragment have been developed in terms of a list of example resource bounds. This paper replaces this list-of-examples approach with a careful investigation of the conditions that suffice for a class Δ to be a resource bound.