After selecting the point a dynamic line is drawn from it to the cursor.
This line is defining the radius of the arc and a dynamic circle is drawn around the centre point through the cursor position allowing you to visualise the size of the arc.
The prompt now reads:
After selecting the point the dynamic line continues to be drawn from the centre point to the cursor. However the radius and the start angle of the arc are now fixed.
As you move the cursor a dynamic arc is drawn in an anti-clockwise direction from the start point around the centre point to the cursor.