Table 9: Observed metallicity index variation for V2109 Cyg together with some known high amplitude $\delta$ Sct-type variables from Rodríguez et al. (1991). $\Delta$ $\delta$ m₁^* means variation of the $\delta$ m₁ parameter per each 0 $.\!\!^{\rm m}$ 1 variation in the $\beta$ index.
Star Period $\Delta V$ [Me/H] < $\beta$ > $\Delta$ $\beta$ $\Delta$ m₁ < $\delta$ m₁> $\Delta$ $\delta$ m₁^*

(days) (mag) (dex)   (mag) (mag) (mag) (mag) (mag)

RS Gru 0.1470 0.49 -0.3    2.76 0.112 0.013 0.035 0.020

RY Lep 0.2254 0.35 0.2    2.71 0.073 -0.011 0.004 0.030

V1719 Cyg 0.2673 0.31 0.5    2.71 0.071 -0.031 -0.015 0.050

V2109 Cyg 0.1861 0.16 0.14   2.740 0.038 -0.002 -0.001 0.032

**Table 9:** Observed metallicity index variation for V2109 Cyg together with some known high amplitude $\delta$ Sct-type variables from Rodríguez et al. (1991). $\Delta$ $\delta$ m₁^* means variation of the $\delta$ m₁ parameter per each 0 $.\!\!^{\rm m}$ 1 variation in the $\beta$ index.
Star	Period	$\Delta V$	[Me/H]	< $\beta$ >	$\Delta$ $\beta$	$\Delta$ m₁	< $\delta$ m₁>	$\Delta$ $\delta$ m₁^*
	(days)	(mag)	(dex)	(mag)	(mag)	(mag)	(mag)	(mag)
RS Gru	0.1470	0.49	-0.3	2.76	0.112	0.013	0.035	0.020
RY Lep	0.2254	0.35	0.2	2.71	0.073	-0.011	0.004	0.030
V1719 Cyg	0.2673	0.31	0.5	2.71	0.071	-0.031	-0.015	0.050
V2109 Cyg	0.1861	0.16	0.14	2.740	0.038	-0.002	-0.001	0.032

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