Как получить значение от виджета?

У меня был вопрос связан с отображением виджета . Но как его переделать чтоб получить значение от виджета ? Сам виджет

wheelbox.cpp:

#include <qlabel.h>
#include <qlayout.h>
#include <qwt_wheel.h>
#include <qwt_thermo.h>
#include <qwt_scale_engine.h>
#include <qwt_transform.h>
#include <qwt_color_map.h>
#include "wheelbox.h"
WheelBox::WheelBox( Qt::Orientation orientation,
        int type, QWidget *parent ):
    QWidget( parent )
{
    QWidget *box = createBox( orientation, type );
    d_label = new QLabel( this );
    d_label->setAlignment( Qt::AlignHCenter | Qt::AlignTop );
    QBoxLayout *layout = new QVBoxLayout( this );
    layout->addWidget( box );
    layout->addWidget( d_label );
    setNum( d_wheel->value() );
    connect( d_wheel, SIGNAL( valueChanged( double ) ),
        this, SLOT( setNum( double ) ) );
}
QWidget *WheelBox::createBox(
    Qt::Orientation orientation, int type )
{
    d_wheel = new QwtWheel();
    d_wheel->setValue( 80 );
    d_wheel->setWheelWidth( 20 );
    d_wheel->setMass( 1.0 );
    d_thermo = new QwtThermo();
    d_thermo->setOrientation( orientation );
    if ( orientation == Qt::Horizontal )
    {
        d_thermo->setScalePosition( QwtThermo::LeadingScale );
        d_wheel->setOrientation( Qt::Vertical );
    }
    else
    {
        d_thermo->setScalePosition( QwtThermo::TrailingScale );
        d_wheel->setOrientation( Qt::Horizontal );
    }
    switch( type )
    {
        case 0:
        {
            QwtLinearColorMap *colorMap = new QwtLinearColorMap();
            colorMap->setColorInterval( Qt::blue, Qt::red );
            d_thermo->setColorMap( colorMap );
            break;
        }
        case 1:
        {
            QwtLinearColorMap *colorMap = new QwtLinearColorMap();
            colorMap->setMode( QwtLinearColorMap::FixedColors );
            int idx = 4;
            colorMap->setColorInterval( Qt::GlobalColor( idx ),
                Qt::GlobalColor( idx + 10 ) );
            for ( int i = 1; i < 10; i++ )
            {
                colorMap->addColorStop( i / 10.0,
                    Qt::GlobalColor( idx + i ) );
            }
            d_thermo->setColorMap( colorMap );
            break;
        }
        case 2:
        {
            d_wheel->setRange( 10, 1000 );
            d_wheel->setSingleStep( 1.0 );
            d_thermo->setScaleEngine( new QwtLogScaleEngine );
            d_thermo->setScaleMaxMinor( 10 );
            d_thermo->setFillBrush( Qt::darkCyan );
            d_thermo->setAlarmBrush( Qt::magenta );
            d_thermo->setAlarmLevel( 500.0 );
            d_wheel->setValue( 800 );
            break;
        }
        case 3:
        {
            d_wheel->setRange( -1000, 1000 );
            d_wheel->setSingleStep( 1.0 );
            d_wheel->setPalette( QColor( "Tan" ) );
            QwtLinearScaleEngine *scaleEngine = new QwtLinearScaleEngine();
            scaleEngine->setTransformation( new QwtPowerTransform( 2 ) );
            d_thermo->setScaleMaxMinor( 5 );
            d_thermo->setScaleEngine( scaleEngine );
            QPalette pal = palette();
            pal.setColor( QPalette::Base, Qt::darkGray );
            pal.setColor( QPalette::ButtonText, QColor( "darkKhaki" ) );
            d_thermo->setPalette( pal );
            break;
        }
        case 4:
        {
            d_wheel->setRange( -100, 300 );
            d_wheel->setInverted( true );
            QwtLinearColorMap *colorMap = new QwtLinearColorMap();
            colorMap->setColorInterval( Qt::darkCyan, Qt::yellow );
            d_thermo->setColorMap( colorMap );
            d_wheel->setValue( 243 );
            break;
        }
        case 5:
        {
            d_thermo->setFillBrush( Qt::darkCyan );
            d_thermo->setAlarmBrush( Qt::magenta );
            d_thermo->setAlarmLevel( 60.0 );
            break;
        }
        case 6:
        {
            d_thermo->setOriginMode( QwtThermo::OriginMinimum );
            d_thermo->setFillBrush( QBrush( "DarkSlateBlue" ) );
            d_thermo->setAlarmBrush( QBrush( "DarkOrange" ) );
            d_thermo->setAlarmLevel( 60.0 );
            break;
        }
        case 7:
        {
            d_wheel->setRange( -100, 100 );
            d_thermo->setOriginMode( QwtThermo::OriginCustom );
            d_thermo->setOrigin( 0.0 );
            d_thermo->setFillBrush( Qt::darkBlue );
            break;
        }
    }
    double min = d_wheel->minimum();
    double max = d_wheel->maximum();
    if ( d_wheel->isInverted() )
        qSwap( min, max );
    d_thermo->setScale( min, max );
    d_thermo->setValue( d_wheel->value() );
    connect( d_wheel, SIGNAL( valueChanged( double ) ),
        d_thermo, SLOT( setValue( double ) ) );
    QWidget *box = new QWidget();
    QBoxLayout *layout;
    if ( orientation == Qt::Horizontal )
        layout = new QHBoxLayout( box );
    else
        layout = new QVBoxLayout( box );
    layout->addWidget( d_thermo, Qt::AlignCenter );
    layout->addWidget( d_wheel );
    return box;
}
void WheelBox::setNum( double v )
{
    QString text;
    text.setNum( v, 'f', 2 );
    d_label->setText( text );
}

Его отображение и по нажатию на кнопку надо получить от него значение : ksp_ecology_water.cpp:

#include "wheelbox.h"
ksp_ecology_water::ksp_ecology_water(QString KPT, double Mkrt, QWidget *parent) :
    _KPT(KPT),
    _Mkrt(Mkrt),
    QDialog(parent),
    ui(new Ui::ksp_ecology_water)
{
    ui->setupUi(this);
    ui->wheelBoxLayout->addWidget(new WheelBox(Qt::Vertical, 0));
}
void ksp_ecology_water::on_pushButton_5_clicked()
{
WheelBox *wheelBox = qobject_cast<WheelBox *>(ui->wheelBoxLayout->itemAt(0)->widget());
Tv = ....;//Температура воздуха, град.
}