Show that PV is working

[fa201]

Either a progress bar undeterminate https://www.pythontutorial.net/tkinter/tkinter-progressbar/
Or a modification of pointer https://stackoverflow.com/questions/59577283/how-to-change-the-cursor-during-a-long-running-task-in-tkinter or https://stackoverflow.com/questions/20411978/pythontkinter-how-do-i-get-cursor-to-show-busy-status

[fa201]

Applicable to curve plotting, curve update, shit / scale / extrema operations

[fa201]

Modification of point does not work for Windows. Strange.

[fa201]

Undeterminate progress bar will be added to the left side of the status bar.