def determine_well_width_tolerance(mean_width):
    """
    Determine the tolerance by which well widths are determined to be nearly equal.

    Fitted to a polynomial trend line for the following data of (mean, tolerance) pairs::

        (100, 0.11), (60, 0.13), (50, 0.15), (25, 0.25), (5, 0.50), (1, 0.59)

    Args:
        mean_width (float): The mean well width in degrees.

    Returns:
        float: The tolerance.
    """
    if mean_width > 100:
        return 0.1
    tol = -1.695e-10 * mean_width ** 5 + 6.209e-8 * mean_width ** 4 - 8.855e-6 * mean_width ** 3 \
        + 6.446e-4 * mean_width ** 2 - 2.610e-2 * mean_width + 0.6155
    return tol