Fission track length histograms from sedimentary samples may contain tracks generated before the time of deposition. They may originate from various source areas with their own thermal histories. After deposition they share thermal history. Inherited tracks, mainly represented by the shortest tracks, are mixed with the young post–sedimentary tracks due to anisotropic annealing, various grain chemistry and uncertainties of measure. Inherited tracks complicate calculating the thermal history. Deconvolution from time sequence analysis [1] is used to separate pre–and post–depositional tracks. Deconvolution reduces the length spread caused by the uncertainties. Hereby tracks are organized according to age, the short tracks being older than the long tracks.