[en] Reasons determining deviations of absolute age values at radiologic dating are considered. Thermal rock annealing in postmetamorphic period is considered to be the main reason. The examples are given enabling detection of warm-up traces by certain signs. The method and its shortcomings are discussed. The dependence of metamorphite dating results on age obtaining method (K-Ar, Rb-Sr, Rb and so on), defficiency and chimism of the studied crystal, monocrystal size, speed, duration and character of complex cooling, annealing temperature, heat effection duration, warm-up cycle quantity and so on is proved. None of the above factors is of any consequences. This testifies to the fact that the use of some chronological and empiric data appears in the whole to be impossible at separation of metamorphism stages and their age determination