$\beta/\nu$ we used that the magnetization at $\beta_c$ should scale for sufficiently large $L$ like [@barber] $$\langle m \rangle \propto L^{-\beta /\nu }.
\label{eq:18c}$$ The slope of the straight line in the log-log plot shown in Fig. 5 of $\langle m \rangle$ vs $L$ at $\beta_c = 0.6930$ gives a value of $$\beta/\nu=0.514\pm 0.001,
\label{eq:18d}$$ with a $Q$-value of 0.68 of our linear least-square fit routine. We noted again that the systematic error of choosing an incorrect $\beta_c$ was larger than the statistical error coming from the fit. For example, for fits of $\langle m \rangle$ at the two inverse temperatures $\beta = 0.6929$ and $\beta=0.6931$ we obtained $\beta/\nu=0.519(1)$ and $\beta/\nu=0.509(1)$ with values $Q=0.30$ and $Q=0.31$, respectively. We take the significant lower $Q$-values as supporting our estimate of $\beta_c$ (compare also Fig. 8 and the discussion of the $Q$-values later in this section). Using our estimate of $\nu = 0.704(6)$ we get for the critical exponent of the magnetization $\beta = 0.362(4)$.

On finite lattices an estimator for the magnetic susceptibility per spin is given by $$\chi^{\rm c} = V\beta  (\langle m^2\rangle  - \langle m\rangle ^2),$$ where the superscript c stands short for “connected”. In the high-temperature phase the true 