def _x2norm(x, xrange, xcenter):
    """ Convert x in data unit to normalized x in [-100: 100] %

    Arguments
        x: float | np1darray
        xrange: float (MHz)
        xcenter: float (MHz)

    Returns
        xp: float | np1darray       in (-1, 1)
    """

    return (x - xcenter) / xrange * 2