def auto_positions_factor_tag_from_auto_positions_factor(auto_positions_factor
    ):
    """Generate an auto positions factor tag, to customize phase names based on the factor automated positions are
    required to trace within one another.

    This changes the phase name 'phase_name' as follows:

    auto_positions_factor = None -> phase_name
    auto_positions_factor = 2.0 -> phase_name__auto_pos_x2.00
    auto_positions_factor = 3.0 -> phase_name__auto_pos_x3.00
    """
    if auto_positions_factor is None:
        return ''
    return '__auto_pos_x{0:.2f}'.format(auto_positions_factor)
