def METHOD_NAME(delta_lbd, lbd_0):
    """Converts (ex: FWHM) from Δnm to Δhz.
    Parameters
    ----------
    delta_lbd: nm
        wavelength broadening
    lbd_0: nm
        center wavelength
    """
    return nm2hz(lbd_0 - delta_lbd / 2) - nm2hz(lbd_0 + delta_lbd / 2)