Why doesn't QGraphicView work correctly?

Question

Qt

Form constructor:

Widget::Widget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::Widget)
{
    ui->setupUi(this);


    scene = new QGraphicsScene;
    draw();
}

Draw function:

void Widget::draw()
{

    ui->graphicsView->setScene(scene);
    scene->clear();
    scene->addRect(startX,carcassStartY,
                       maxX*scale,carcassMaxY*scale,
                       QPen(Qt::red, 0),QBrush(Qt::red));
}

Where is the draw called from?

void Widget::on_horizontalSlider_sliderMoved(int position)
{
    scale = position;

    draw();
}

The problem is that when the slider is moved (i.e., the scale changes), the starting point x, y changes, which, as it were, is not indicated in the code. But when the figure climbs out of the field, there are no such changes, everything works correctly.