  We present a complete analysis of the Nernst signal due to superconducting
fluctuations in a large variety of superconductors from conventional to
unconventional ones. A closed analytical expression of the fluctuation
contribution to the Nernst signal is obtained in a large range of temperature
and magnetic field. We apply this expression directly to experimental
measurements of the Nernst signal in Nb$_x$Si$_{1-x}$ thin films and a
URu$_2$Si$_2$ superconductors. Both magnetic field and temperature dependence
of the available data are fitted with very good accuracy using only two fitting
parameters, the superconducting temperature $T_{\mathrm{c0}}$ and the upper
critical field $H_{\mathrm{c2}}$. The obtained values agree very well with
experimentally obtained values. We also extract the ghost lines (maximum of the
Nernst signal for constant temperature or magnetic field) from the complete
expression and also compare it to several experimentally obtained curves. Our
approach predicts a linear temperature dependence for the ghost critical field
well above $T_{\mathrm{c0}}$. Within the errors of the experimental data, this
linearity is indeed observed in many superconductors far from
$T_{\mathrm{c0}}$.
