Hi Martin,

> I didn't find some cursors to measure between different points in a plot.
> Are there cursors or are there plans to implement something like this?
> Otherwise I'm interested in implementing a feature like this.
> Who is responsible for questions like this?
we don't have this feature yet and there are no plans at the moment to 
implement this for the next release 2.6. The current activities, new features 
and TODOs are documented in
https://phabricator.kde.org/T8630
https://phabricator.kde.org/source/labplot/browse/master/ChangeLog

But the final amount of new features is subject of changes. We're flexible :-) 
If you can help here, this would be great.

If you have a patch, upload it on phabricator and we can discuss it there. We 
can also discuss the details of the implementation in private email 
communications before you upload the patch.

To get a first idea for how to implement this maybe, have a look at 
CartesianPlotPrivate::mouseMoveEvent() in CartesianPlot.cpp. While being in 
the "select&zoom mode" (switch to this "cursor" in the plot toolbar, select a 
region in the plot and zoom into the data upon mouse release) we calculate 
already deltaX and deltaY and show these values in the status bar during mouse 
movements. Similar logic/code can be used for the feature you're proposing.

Best Regards,
Alexander