plot_wfdb: if plotting digital values, show units as "adu".
plot_wfdb: if plotting digital values, show units as "adu".

If we are plotting digital (d_signal) values, then the values on the Y
axis are ADC units, not physical units.  Don't label the axes as
physical units, and don't try to calculate grid lines as if ADC units
were physical units.

MIT-LCP/wfdb-python