It has also been noted that the numerical estimates of cosmic parameters in Einstein's 1931 paper – and on the blackboard – contain a systematic error. Analysis of the 1931 paper shows that, given the contemporaneous Hubble constant of 500 km s Mpc, Einstein's estimates of cosmic density, radius and timespan should have been ρ ~ 10 g/cm, P ~ 10 light-years and t ~ 10 years respectively. One line on the blackboard, not included in the published paper, makes the nature of Einstein's error clear. In the fourth line on the blackboard, Einstein obtains a value of 10 cm for the quantity D, defined in the top line of the blackboard as