Similar to the Oscilloscope, the active channels shown in the Moku App have a darker line trace that denotes the amplitude and the shaded area below it is the area under the curve. In the picture below, both channels are active in the Data Logger for the logging session.
The Data Logger graph window is limited to a span of a 10 seconds. This means that the graph window is not well suited for viewing short signals, like pulses. For example, if I wanted to log a 10 kHz pulse for 10 seconds, the Data Logger graph window would look similar to the figure below. It is hard to tell what the actual signal looks like due to the large span, but the logging rate is above 100 kSa/s, so the data being logged will be accurately graphed in something like MATLAB.
You may also notice that the dark trace for the selected channel is covering a range of a few millivolts to tens of millivolts. This is because the acquisition mode is set to Normal, which downsamples the ADC data. Changing the acquisition mode to Precision will improve accuracy.