def METHOD_NAME(default_surface):
    small = xtgeo.RegularSurface(**default_surface)
    so2 = xtgeo.Surfaces()
    for _ in range(10):
        tmp = small.copy()
        tmp.values += 8.76543
        so2.append([tmp])
    res2 = so2.statistics(percentiles=[10, 50])
    assert res2["p10"].values.mean() == pytest.approx(16.408287142, 0.001)