Uncertainty of perihelion distance a), semi-major axis b), eccentricity c), argument of perihelion d), longitude of asceding node e), inclination to the ecliptic f), and time of perihelion passage g) when reconstructing the orbit of comet 96P backward for 5 millennia. The backward evolution of any given element is shown with the help of cloned orbits differring by 1-σ from the nominal value (see the text of Sect. 3).