\equiv 1/T^{\times}$ of two different curves $U_L(\beta)$ and $U_{L'}(\beta)$ depend on the scale factor $b=L'/L$, due to the residual corrections to FSS [@bi82]. To have enough data points for a straight line fit we used only the crossing points of the $L$=12 and $L$=16 curves with all the other ones with higher $L'$-value, which gave us 6 and 5 data points, respectively. The two least-square extrapolations in the plot of $T^{\times}$ vs $1 / \log b$ shown in Fig. 3 are consistent with each other and gave us the values $\beta_c = 0.69297(9)$ and $\beta_c = 0.69298(13)$ respectively. Combining the two values we obtained $$\beta_c = 0.6930 \pm 0.0001.    \label{eq:16}$$ The errors on $T^{\times}$ were obtained by using the crossings of $U_L(\beta) + \Delta U_L(\beta)$ with $U_{L'}(\beta) - \Delta U_{L'}(\beta)$, where $\Delta U_L$ are the errors on $U_L$ obtained via the jackknife procedure. Our result (\[eq:16\]) is in good agreement with the value given in ref. [@r18], $\beta_c = 0.6929(1)$, but significantly higher than estimates from analyses of high-temperature series expansions [@rf; @series2].

A similar analysis [@bi82] was used to determine $U^*$, which resulted in $U^*=0.62175(35)$ and $U^*=0.62141(75)$, repectively, from which we extract the final estimate $$U^{*} = 0.6217 \pm 