With the exception of the radiocarbon method, most of these techniques are actually based on measuring an increase in the abundance of a radiogenic isotope, which is the decay-product of the radioactive parent isotope.
It is important not to confuse geochronologic and chronostratigraphic units.
In the same way, it is entirely possible to go and visit an Upper Cretaceous Series deposit - such as the Hell Creek deposit where the Tyrannosaurus fossils were found - but it is naturally impossible to visit the Late Cretaceous Epoch as that is a period of time.
The polarity timescale has been previously determined by dating of seafloor magnetic anomalies, radiometrically dating volcanic rocks within magnetostratigraphic sections, and astronomically dating magnetostratigraphic sections.
Global trends in isotope compositions, particularly Carbon 13 and strontium isotopes, can be used to correlate strata.
Two methods of paleomagnetic dating have been suggested (1) Angular method and (2) Rotation method.