QwtPlotCurve. How to draw a line color?

[PROkaZZZnik]

Good afternoon, dear colleagues.
I have a question, in how to add some inscription, to the legend.
Let's say I draw some kind of graph. I need to give out the radius of the circle on the right, etc. How best to do this? My only assumption is

QString S = "Rad =";
    S=S+R;
    QwtPlotCurve *curve = new QwtPlotCurve(S);
    curve ->setPen(Qt::black,2);

QString S = "Rad =";
    S=S+R;
    QwtPlotCurve *curve = new QwtPlotCurve(S);
    curve ->setPen(Qt::black,2);

To copy to clipboard, switch view to plain text mode 

Is it possible to somehow display their information in this area?
And how can you control its geometry (indentation)
Thank you.