[Cin] Histogram plugin

[Andrea paz]

I was rereading the manual about the Histogram plugin and there are
things that I don't understand:
1- Is there no longer a frame interval averaging function (Frames
button)? When was it taken out? Perhaps on this occasion?
https://www.mail-archive.com/cin@lists.cinelerra-gg.org/msg02691.html
(moreover, the images are to be replaced)
2-I don't quite understand the concept of "Sum" instead of "max." The
explanations are not clear to me. Can anyone clarify to me the
behavior of the plugin with respect to Histogram Bezier, scopes and
various color models?
The explanation in the manual (section: Theory) is taken from here:
https://www.mail-archive.com/cin@lists.cinelerra-gg.org/msg01834.html