Genady

I don't get to that point because I can't get over the previous one.

Yes, it's correct. Notice the corrected expressions in my post. Sorry for that.

x=ct ct/x = 1 equivalently, c=1, v in units of c

The red line should not be parallel to the yellow line of the signal. The yellow lines have to be at 450.

It's your statement. You need to show, how the second part follows from the first.

The second part doesn't follow from the first.

"therefore" has been inserted here without a reason.

While you're resting, may I recommend these free and fun online presentations, which give good explanation for and practice in spacetime diagrams and Lorentz transformations (with Spanish subtitles available): Understanding Einstein: The Special Theory of Relativity | Coursera

It does not matter. A is not a midpoint in the B frame.

Yes, this is clear.

It looks incorrect. Why the three points A, B, and C are on a straight line? And why A is in the middle of that line?

@martillo, The spacetime diagrams are good for qualitative comparisons between events and frames, but to get quantitative comparisons you will have to calculate Lorentz transformations.

And A? Wait, D is signal reception...

I understand that event D is "Observer C receives the signal". What are the events A, B, and C on this diagram?

If you are assuming this, then B and C are not symmetrical, and I can prove it. Since they are not symmetrical, when they meet their clocks and beards will not be equal.

Yes, this is the problem. But we keep trying not to let him do this . PS. I have to go now. We'll be back in about an hour, I think. Otherwise, good night to all.

OK, but note that it is not the same v that appeared in the Lorentz Jr's calculations. So, we got the diagram with observers B and C which meet at some event up there and with C moving toward B with velocity v. What else do we know? Exactly. But in B frame, C moves toward A slower than A moves toward B and yet they meet all together. Thus, C has to be closer to A than B.

If they are equidistant from A in A then they are not equidistant from A in B, at any moment in B. So, what is v? Velocity of which frame relative to which frame? C relative to B? Something else?

I think it will be better if you answer, make mistakes, discuss, and fix them. We already know that Lorentz Jr knows how to solve this. What midpoint? In B frame?

What is A?

The velocity relative to what?

What is v in the current formulation?

No, it does not. Why would you think so? There is nothing confusing about this diagram, unless one reads into it more than it shows. B and C on the diagram are not events. They mark world lines of observer B and observer C, i.e., the lines, one vertical and the other one tilted. There is no even a mark for t=0. The horizontal line is just a line of events simultaneous in B. I shouldn't even call it x axis, just x line. At some moment in B, the observers B and C are on this line, in the events where it intersects with the world lines of B and C. There is nothing to review, but there is a lot to add to this diagram. Better be done step-by-step. Poco poco.

I don't know what you mean, initially. It just shows that at some moment in B frame, they are on the x axis.

Yes. 5-10 minutes... @martillo: