The documentation is a little unclear.
"Always return non-negative value from any operation input 2
between input 1
."
https://www.blender.org/manual/render/blender_render/materials/nodes/types/converter.html
I'd expect the node to ignore the second value altogether, and just give you the absolute value of whatever you piped into the left side. But it's not clear how this node deals with two values. Does it ignore the non-piped value? Does it ignore the second value, regardless? Does it give you whichever input is non-negative? How does it handle two inputs? What "operation" is performed between the two inputs?
What does the "Absolute" setting actually do?