HP 510 - Manual (Page 158)

Changing the treatment of overlapping lines (merge)
The Merge setting controls the overlapping lines in an image. There are two settings, Off and On. The following
illustration shows the effect of each setting.
You can set the merge setting from your software in some applications. Settings in your software override the
front-panel settings.
Merge on Merge off (Default)
A subsequent line hides a
previous line where they
overlap.
Overlapping lines and area
fills are merged.