Table 4.

Standard addition activity ratio measurement results

Quantities	Counter B	Counter H
$\epsilon A_X$	1347.9	1369.4
$\epsilon A_S$	245.57	249.98
$S_{\text{X}}^2$	0.08892	0.6583
$S_S^2$	0.008953	0.03474
$S_{\text{XS}}$	− 0.01646	− 0.07668
$A_X/A_S$	5.4888	5.4780
S	0.0030	0.0067
Grand mean	Massic activity ratio 5.4834	SD 0.0087

The fitted parameters $\epsilon A_{\text{X}}$ and $\epsilon A_S$ are for the ²²⁹Th RM and SRM 4328C solutions, respectively, with corresponding variances $S_{\text{X}}^2$ and $S_{\text{S}}^2$ and covariance $S_{\text{XS}}$. The estimator S is the propagated standard deviation of the $A_{\text{X}}/A_{\text{S}}$ massic activity ratio