def _get_grid_limits(headers):
    """
    Return a two-length tuple that contains the lower limits of the grid and the upper limits of the grid.

    :param headers:
        The primary headers from a FERRE grid file.
    """
    return (
        headers["LLIMITS"],
        headers["LLIMITS"] + headers["STEPS"] * (headers["N_P"] - 1)
    )