The output from an analogue instrument can, and usually does contain a constant DC voltage. When this output is digitized, it is represented as a numerical offset which is not usually of any significance. In order that waveforms be displayed on a large scale, this offset must be compensated for. This is done by subtracting a constant from each sample as it is plotted.
Press the 
button or ‘N’ key to initiate the automatic offset calculation for each stream. This affects only the view in the current window, and only waveforms which have not been locked. Other WaveView windows can use different offsets for the same stream. The offset is calculated as the average value for all data within the timespan of the waveview window for each stream.
The offset can be controlled manually using the Details Window for an individual stream. To open the Details window, right-click on the stream, and select the ‘Details’
option (or press 'd'). Typing a number into the Offsets box and pressing ENTER will change the offset value used to display that stream, in that waveview window only.
Alternatively, with the focus on the offset box, you can use the up/down
arrow keys for small adjustments, and page-up/page-down keys for large
adjustments.
Automatic adjustment of the offsets can be accomplished by enabling the "Null before capture" option of the Auto-Screenshot feature.