An experience has been summarized on the using of polynomial least squ
ares technique usually applicable in calculations of age and initial i
sotope ratio from experimental data in isotope geochronometry. Origina
l computational technique has been given to calculate errors in isochr
ones calculation in different coordinate systems. This technique consi
der deviations of experimental points from linear dependence due to an
alytical errors and isochrone model violation caused by geochemical ef
fects. It has been shown that probability density isolines form ellips
es in coordinates (1 - e(lambdaT)) - Sr-87/Sr-86 whose location on thi
s plot shows age and genetic relationships of the studied geological o
bjects.