Table 2.

Electrical conductivity obtained with ERT, TDS and vdP methods on samples S40 and S28.

Sample	${\sigma }_{\mathrm{ERT}}^{\square }$		${\sigma }_{\mathrm{TDS}}^{\square }$		σ vdP
S40	2.531	2.669	2.663	2.565	2.880 [2.38–3.23]
S28	2.050	1.323	2.214	2.878	1.631 [1.16–2.98]

Symbols are defined in Table 1. The vdP value σ_vdP is measured choosing contacts close to the four corners; the interval includes the values measured with the other electrode configurations. All values are expressed in mS.