def METHOD_NAME(self, dx=0.1):
    """
    Jerome peux-tu décrire de quoi il retourne ???
    :param dx: ???
    :type: float ???
    :return: ???
    :rtype: ???
    """
    f = self.ai.getFit2D()
    fp = f.copy()
    fm = f.copy()
    fm["centerX"] -= dx / 2.0
    fp["centerX"] += dx / 2.0
    ap = AzimuthalIntegrator()
    am = AzimuthalIntegrator()
    ap.setFit2D(**fp)
    am.setFit2D(**fm)
    dtthX = (ap.twoThetaArray(self.shape) - am.twoThetaArray(self.shape))\
        / dx
    tth, I = self.ai.xrpd(self.img, max(self.shape))
    dI = SGModule.getSavitzkyGolay(I, npoints=5, degree=2, order=1)\
        / (tth[1] - tth[0])
    dImg = self.reconstruct(tth, dI)
    return (dtthX * dImg).sum()