Dating archaeological artifacts
In other words, artifacts found in the upper layers of a site will have been deposited more recently than those found in the lower layers.
With the introduction of objective quantifiable methods such as dendrochronology and Carbon-14 dating, over the past half century, European and North American archaeology have developed independent and more reliable chronologies, that often make it possible to date more precisely than in Egypt. For Egypt absolute year dates can only be established back to the beginning of the Late Period, from links to Greek chronology, and then from Assyrian king-lists and other Near Eastern sources, back to the Ramesside Period (still debated). The Egyptians dated by the year of reign of the king on the throne (for example 'year 3 of king X').
If we knew the precise length of reign for every Egyptian king, chronology would be no problem.
However, we do not even know the number of kings for all periods, and there is also the possibility that reigns overlapped by coregency or in times of political disunity.
The style of the artefact and its archaeology location stratigraphically are required to arrive at a relative date.
For example, if an artefact, say an oil lamp, is found co-located on the same floor of a governor's dwelling, and that floor can be dated in archaeology terms by reason of the patterns employed in the mosaic, then it is assumed that in relation to the floor that the lamp is of the same age.