scale_topo.py

fig = plot_topo(evokeds, ...)
ax = fig.get_axes()[1]  # pick one of the sensor axes
bbox = ax.get_window_extent().transformed(fig.transFigure.inverted())
width, height = bbox.width, bbox.height

# Add the scale
ax = plt.axes([0.08, 0.08, width, height])

ax.tick_params(axis='y', direction='out')
ax.tick_params(axis='x', direction='out')
ax.spines['top'].set_visible(False)
ax.spines['right'].set_visible(False)
ax.xaxis.set_ticks_position('bottom')
ax.yaxis.set_ticks_position('left')
ax.set_xticks([])
ax.set_yticks([])

ax.set_xlabel('1.0 s')
ax.set_ylabel('40 fT/cm')