def vapour_pressure(svp, rh):
    """
    Computes the vapour pressure :math:`e_a` in [mbar]

    .. math ::
        e_{a}=\\frac{\\phi}{100}e_{s}

    Parameters
    ----------
    svp : float
        saturated vapour pressure
        :math:`e_s`
        [mbar]
    rh : float
        relative humidity
        :math:`\\phi`
        [%]

    Returns
    -------
    vp : float
        vapour pressure
        :math:`e_{a}`
        [mbar]

    Examples
    --------
    >>> from ETLook import meteo
    >>> meteo.vapour_pressure(rh=75, svp=meteo.saturated_vapour_pressure(20))
    17.537109531955842

    """
    return 0.01 * rh * svp
