Compositing CGI with Bigger Node Trees - Nuke 101: Professional Compositing and Visual Effects - page 122

Now for the next pass—the Inc pass (short for Incidence pass).
23. Select the horizontal line of nodes that starts with the Dot and ends with Merge1;
press Ctrl/Cmd-C to copy it (it's highlighted in Figure 3.34 ) .
24. Select the Dot at the bottom right of the tree and press Ctrl/Cmd-Shift-V to paste.
Note
You held Shift to branch a copy of the above group of nodes rather
than insert.
25. Drag the newly pasted nodes down a little and connect Merge2's B input to
Merge1.
26. Double-click Shuffle3. Click Shuffle3's In property's drop-down menu and
choose Inc.
27. Double-click Merge2. From the Operation property's drop-down menu choose
Plus (plus, meaning: to add).
You have just added the Inc pass to the composite. You'll need to color correct it,
but first you'll finish adding the rest of the passes ( FIGURE 3.35 ).
Figure 3.35. With a few changes, each of these lines will represent a pass.