  Methods for extracting the $\psi(3770)\to e^+e^-$ decay width from the data
on the reaction cross section $e^+e^-\to D\bar D$ are discussed. Attention is
drawn to the absence of the generally accepted method for determining
$\Gamma_{\psi(3770)e^+e^-}$ in the presence of interference between the
contributions of the $\psi(3770)$ resonance and background. It is shown that
the model for the experimentally measured $D$ meson form factor, which
satisfies the requirement of the Watson theorem and takes into account the
contribution of the complex of the mixed $\psi(3770)$ and $\psi(2S)$
resonances, allows uniquely determine the value of $\Gamma_{\psi(3770)e^+e^-}$
by fitting. The $\Gamma_{\psi(3770)e^+ e^-}$ values found from the data
processing are compared with the estimates in the potential models.
