If this an open curve then it is clear that the 'highlighted point' is the origin of the abscissa - toggle as required.
This is NOT clear if one plots a quantity around a hole. The start is also the end ... which way does the graph go? Clockwise? Anticlockwise? Is the 'highlighted point' the lefthand side or the righthand side of the graph?
Either provide a message that tells the user how to work this out or better to avoid human error, provide an arrow - vis magenta direction arrow for beams - that can be toggled.