To date artifacts most accurately, archaeologists need the context in which artifacts lie in the ground to be undisturbed. This context may then be excavated to find associations between the artifacts and the organic materials required for radiocarbon dating. A secondary dating method, a rule-of-thumb chronological framework of time periods, may be used when an artifact’s context is not known, as often occurs for artifacts in museum collections. This framework is based on changes in the shape, size, and manufacturing techniques of projectile points (spear points and arrowheads) over time- changes that are known by the dating of projectile points from excavated contexts. These changes are known as typology, and the typological identification is crucial to the dating. Other types of artifacts that retain the same shape over long periods of time are less certainly dated when out of context.