How to watch your long track in real time when you draw your track ? It’s possible ?
I want to route a differential pair. Another question ? what is the acceptable tolerance based on frequency and length for a differential pair ?
I am not sure what the question is.
When routing a differential pair (or a “normal” track) you normally make some intermediate clicks so you do not have a lot of intermediate and unfixed segments for the interactive router to choke on. The interactive router does get better at things like this in each KiCad version.
If your question is related to length matching (KiCad does not have real delay matching (yet)) Length tuning / matching is done in a separate step by adding “tuning pattern” boxes afterward. KiCad is not very sophisticated yet for length tuning and differential pairs. For example the interactive router disregards differential pairs when shoving things aside, and just treats them as separate tracks. This destroys both the pair coupling and changes the length of the tracks of the differential pair wires.
These “Tuning pattern boxes” have become more sophisticated in KiCad V8. You can now first place such a box, and then adjust it’s length, with, and “frequency” of the squiggles later.
If this does not answer your question, then try to formulate your question more precise.
Ok I’m not clear sorry. I want to trace 2 tracks with the same length or almost. And my question it’s possible to see my length when i draw my track ? If you have any tips for drawing or controlling differential pairs, I would like to have them.
You say that kicad work at calcul signal delay for futur update ?
thank for your answer
There is an open issue for delay matching, but it’s already open for 6 years, so don’t hold your breath. You can give it an upvote of course, current count is 19 
For the length matching, this is a separate step as I wrote before. So first draw your differential pair or pairs, and then start doing the length matching. During the length matching, KiCad shows the actual length in real time, and you can set a target length. The basics for length tuning are described in KiCad’s manual. Ask more questions if you can’t figure out how that works.
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You want a dual-window view? So that you can see an overview or the board and also a close view as you route the trace? It’s a good idea, but not implemented yet.
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