Tera–Wasserburg diagram

The axes of the Tera–Wasserburg diagram are the amounts of ^{₂₀₇}Pb (a stable, radiogenic isotope unconnected with uranium series decay) and ^{₂₃₈}U (the start of the uranium series decay chain), each adjusted and expressed as ratio to the amount of ^{₂₀₆}Pb (the stable end product of the uranium series).

One feature of the Tera–Wasserburg diagram is that for samples whose original lead content was both high and of unknown isotopic composition, the plotted points may lie on an isochron whose intersection with the ^{₂₀₇}Pb/^{₂₀₆}Pb axis gives the original lead composition and whose intersection with the concordia curve yields the age.