This is what Sternberg (195) has referred to as a "regional pattern-matching method" of dating because the sample direction is compared to the pattern of regional secular variation, via the reference curve, in order to determine the best date range.
Then the discs and the small blocks of soil attached beneath them are carefully removed.
In the lab afterwards, the difference in orientation between the line showing the present magnetic pole and the orientation of the magnetised particles in the soil, reflecting the pole's position at the time of burning, can be determined.
Directional dating can sometimes be as good as ±25 years.
Magnetic reversal stratigraphy has been useful in dating hominid sites for paleoanthropologists, with precisions of about ±0.01 Ma, or 10 ka.
In contemporaneity studies, or relative dating, sample VGPs are compared to each other to determine whether they are statistically different at the 5% significance level.
The same statistical tests (Mc Fadden and Lowes 1981: equations 23 and 25) are used for both statistical dating against a curve and contemporaneity studies.
Small samples of soil or burnt building materials are prepared in situ by having small plastic discs glued to the surface of the layer.
The discs are marked with a line which points towards the present position of the magnetic pole - which is measured with a highly accurate compass.
When the sediments cool, the orientations are fixed and remain as a "thermoremanent magnetic moment" (TRM).