On the one level, events and individuals are placed in an absolute chronology: the exact years and sometimes even months and days of the events and biographies are known.
On the other level, the exact years may not be known, but it is known that one feature is earlier or later in relation to another; this is typically the case on an excavation, where the different archaeological strata allow objects found to be placed in a relative historical framework.
It must be made clear at the outset that typology is not, strictly speaking, a dating method, but a means of placing artefacts into some kind of order.
All dating methods have advantages and disadvantages.
Sometimes we have no choice since only one method can be applied to our particular site.
Scientific methods are generally comparatively expensive to carry out and also result in damage to the object being dated.
Some (such as archaeomagnetism) can only be carried out on site while the excavation is in progress.
This principle presumes that the oldest layer of a stratigraphic sequence will be on the bottom and the most recent, or youngest, will be on the top.