The center-of-gravity rule is tested for heavy and light-quark mesons. In the heavy-meson sector, excellently satisfied. suggests that $a_0(980)$ could be spin-partner of $a_2(1320)$, $a_1(1260)$, $b_1(1235)$; $f_0(500)$ $f_2(1270)$, $f_1(1285)$, $h_1(1170)$; $f_0(980)$ $f_2'(1525)$, $f_1(1420)$, $h_1(1415)$. From decay production light scalar mesons we find a consistent mixing angle $\theta^{\...