Stratigraphy is a chronometric dating method
Two broad categories of dating or chronometric techniques that archaeologists use are called relative and absolute dating.
Stratigraphy is the oldest of the relative dating methods that archaeologists use to date things.
Some degree of dating objects by their position in the sequence can be made with known datable elements of the archaeological record or other assumed datable contexts deduced by a regressive form of relative dating which in turn can fix events represented by contexts to some range in time.
For example, the date of formation of a context which is totally sealed between two datable layers will fall between the dates of the two layers sealing it.
It is the archaeologist's role to attempt to discover what contexts exist and how they came to be created.
If we know the date of context 1 and context 9 we can deduce that context 7, the backfilling of pit 8, occurred sometime after the date for 9 but before the date for 1, and if we recover an assemblage of artifacts from context 7 that occur nowhere else in the sequence, we have isolated them with a reasonable degree of certainty to a discrete range of time.These artifacts are referred to as "residual" or "residual finds".It is crucial that dating a context is based on the latest dating evidence drawn from the context.The production of phase interpretations is the first goal of stratigraphic interpretation and excavation.Archaeologists investigating a site may wish to date the activity rather than artifacts on site by dating the individual contexts which represents events.