When measuring the length, the path first is split into linear segments, whose lengths are added. Depending on the tolerance the linear segments are smaller or longer. Longer ones (high tolerance) will of course not perfectly represent the length of that path. See the figure in the “General Approach” section of https://en.wikipedia.org/wiki/Arc_length
Don’t be afraid of searching the JUCE codebase (modules directory) for variables, methods etc and looking at the code. They did a very good job in keeping the code readable
Thanks, yes I always search direct Juce code if I don’t understand something. But due to my low programming skills very often oryginal code is hard to understand for me.
So thanks for explanation.