**Table 1:** The values for $\dot{P}/P$ of Cyg X-3, derived by fitting two different models to the observations. A parabolic ephemeris assumes $\ddot{P} = 0$ , whereas in the cubic ephemeris a second derivative of the period unequal to zero is also taken into account.
$\dot{P}/P$ , fitted value	$\chi^2_{\rm red}$	Reference
(10^-6 yr^-1)
Parabolic ephemeris
$2.2 \pm 0.3^\dagger$	1.41	van der Klis & Bonnet-Bidaud (1981)
$2.19 \pm 0.05^\dagger$	0.78	Kitamoto et al. (1987)
$1.6 \pm 0.1$	1.55	van der Klis & Bonnet-Bidaud (1989)
$1.2 \pm 0.4$	2.07	Kitamoto et al. (1995)
$1.05 \pm 0.04$	3.08	Singh et al. (2002)
Cubic ephemeris
$4.0 \pm 0.6$ $^\dagger$	1.36	van der Klis & Bonnet-Bidaud (1989)
$2.9 \pm 0.2$ $^\dagger$	1.46	Kitamoto et al. (1995)
$1.4 \pm 0.3$ $^\dagger$	2.96	Singh et al. (2002)

$\dagger$ Value not quoted in the paper cited, but calculated
by us from the published values of P and $\dot{P}$ .

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