The analog graphs in the Saleae software use a very simple auto-range feature to determine the view-able voltage range.
This voltage range currently cannot be edited by the user, but this is subject to change in future releases. Feel free to suggest features for the analog display on our idea and feature tracking site, http://ideas.saleae.com.
The analog display auto zooms into the analog data based on the minimum and maximum values observed over the entire data set. If you zoom out so that the entire capture is displayed on screen, you should be able to see the minimum and maximum points on the graph.
The graph also shows dotted lines for the minimum and maximum integer voltages displayed on the graph.
The graph will always span at least 1 integer volt in height. To zoom in further than this, we recommend using the channel size control to make the channel as tall as possible.
See "Changing Channel Size" in the users guide: Navigating Your Data (zooming, panning, re-arranging, re-sizing etc)
Recent investigation shows that the software does not always select the best voltage display range on the input signal. This will be improved in the next release.
The current system:
low voltage line = round( minimum voltage in capture ) high voltage line = round( maximum voltage in capture )
if low voltage line == high voltage line high voltage line = low voltage line + 1V.
The new system will use floor and ceiling appropriately.
trello ID: 564e5eaf19c811a3388eef2f