def set_labels(ax, histogram):
    """ define the axis labels """
    if histogram.has_uniform_bins():
        ylabel_suffix = f' / {histogram.bin_width} {histogram.unit}'
    else:
        ylabel_suffix = f' / bin'
    ax.set_ylabel(f'Events{ylabel_suffix}', horizontalalignment='right', y=1.0)
    return 0
