arrow::pdraw(CM, CM, 3*CM, 4*CM).linewidth(MM).headangle(10);     // draw an arrow into the current pad

arrow *a = &arrow::fdraw(x1len(2),y1len(3),x1len(10),y1len(15));  // create an arrow in the current frame,
                                                                  // from the coordinates (2,3) to (10,15)