Source: record ecgiddb/Person_01/rec_6
val has 2 rows (signals) and 10000 columns (samples/signal)
Duration:     0:20
Sampling frequency: 500 Hz  Sampling interval: 0.002 sec
Row	Signal	Gain	Base	Units
1	ECG I	200	0	mV
2	ECG I filtered	200	0	mV

To convert from raw units to the physical units shown
above, call the 'rdmat.m' function from the wfdb-matlab
toolbox: https://physionet.org/physiotools/matlab/wfdb-app-matlab/