What’s a good method of showing user progression of a dynamic questionaire with a varying amount of questions?

What are the best practices around showing the length and stage in a questionnaire, where the length of said questionnaire changes and branches dynamically based on answers? I’m going to create a questionnaire where the user sees one question at a time. I want the user to get some sort of sense of how much longer they have and their place in the process but without misleading them. I don’t want them to think a single questionnaire could have 50 questions to answer. But to give a tangible number, they could have have to answer 7 questions or it could have 15 questions for them to go through depending on their answers.

Color contrast too low, but element good visible

I am checking a software against the software ergonomic requirements of WCAG 2.1 Level AA. On part is the colour contrast, which must be for graphics 3.0:1. In the following graphic the orange part is for users without any disabilities very good visible, however the tool “Color Contrast Analyser” show only a contrast to the white background of 2.0:1.

So the graphic does not meet WCAG 2.1 Level AA. But what is the reason? Again: the orange part of the graphic is very good visible. Might it be an inaccuracy of algorithm for calculating colour contrast? Or is it just my personal sensation?

Any other ideas?

graphic with red, orange and green skala. medium value is 38.

Looking for good book similar Stability/Conditioning in Numerical Linear Algebra,

I am currently reading Numerical Linear Algebra by Trefethen and Bau and I am finding it quite difficult to read. In particular, I have been trying to read the sections on Floating Point Arithmetic, Stability, and Conditioning, and they are pretty confusing to me; it has taken me 3-4 hours to go through the four pages on floating point arithmetic, and there are still a couple things I am unclear on.

I am looking for a book which goes over similar material as Trefefthen and Bau, but which fleshes things out a bit more.

My background is: I am a student of pure mathematics. I am a complete layman when it comes to computers.