import matplotlib.pyplot as plt
from basic_units import cm

fig = plt.figure()
ax = fig.add_subplot(111)


ax.annotate( "Note 01", [0.5*cm,  0.5*cm] )

# xy and text both unitized
ax.annotate('local max', xy=(3*cm, 1*cm),  xycoords='data',
            xytext=(0.8*cm, 0.95*cm), textcoords='data',
            arrowprops=dict(facecolor='black', shrink=0.05),
            horizontalalignment='right', verticalalignment='top')

# mixing units w/ nonunits
ax.annotate('local max', xy=(3*cm, 1*cm),  xycoords='data',
            xytext=(0.8, 0.95), textcoords='axes fraction',
            arrowprops=dict(facecolor='black', shrink=0.05),
            horizontalalignment='right', verticalalignment='top')


ax.set_xlim(0*cm, 4*cm)
ax.set_ylim(0*cm, 4*cm)
plt.show()