What's the logic of function clamp in material editor?

In the lecture “Tinted Glass Part 3 - Fresnel Function and Planar Reflections” of this course, I need to create a glass that i can change the opacity of the edge of glass.

The logic showed in course in material editor and the vertexe color shows below.

It‘s confuse me that the output of “SceneColor clamp to 0” is always equal to (1,1,1) and the vertex color of surface is (0,0,0), so for the surface of the glass, when “Edge Opacity” >=0, the output of Clamp should equal to 0.95.
However, when I use a constant number 0.95 to connect to “Opacity”. The opacity of the surface shows different from using the logic in course.

The tutorial was written for the version 4.21, so a lot has changed since then. What I would do is to mask the side of the table and have another mask for the other surfaces. Then I would add them together, but have a subtract connected to a scalar to control the mask brightness / opacity. This all then feeds into the opacity.