Editing Three-age system (section)

=== Grand systems of layering ===
The initial comparisons of artifacts defined periods that were local to a site, group of sites or region.
Advances made in the fields of [[seriation (archaeology)|seriation]], [[Typology (archaeology)|typology]], [[Stratification (archeology)|stratification]] and the associative dating of [[artifact (archaeology)|artifacts]] and features permitted even greater refinement of the system. The ultimate development is the reconstruction of a global catalogue of layers (or as close to it as possible) with different sections attested in different regions. Ideally once the layer of the artifact or event is known a quick lookup of the layer in the grand system will provide a ready date. This is considered the most reliable method. It is used for calibration of the less reliable chemical methods.