I read values from a file, calculate delta from previous to current and use draw_line in _draw from previous Vector2 to current Vector2. The Vector2 are stored in a list/array and all lines are redrawn at each interval.
But after a short time, a minute or so, the values in Godot diverge. I confirm accurate values from a python program.
I thought it might be some rounding like floor/ceiling but ruled that out and made sure I use floats.
Since I don't know what's going wrong I can only guess that there is some kind of caching or some math errors in Godot.
The calculation I do is simply: