def delta_t_formula_stephenson_morrison_hohenkerk_2016(tt, fraction):
    """∆T long-term parabola from Morrison, Stephenson, Hohenkerk 2016."""
    t = (tt - 2387626.25 + fraction) / 36525.0  # centuries before/after 1825
    return -320.0 + 32.5 * t * t