*Item use meanValue from parent

GUI/Model/Beam/BeamWavelengthItem.cpp

@@ -25,8 +25,3 @@ void BeamWavelengthItem::readFrom(QXmlStreamReader* r)
 {
     BeamDistributionItem::readFrom(r);
 }
-
-double BeamWavelengthItem::wavelength() const
-{
-    return BeamDistributionItem::meanValue();
-}

GUI/Model/Beam/BeamWavelengthItem.h

@@ -21,7 +21,6 @@ class BeamWavelengthItem : public BeamDistributionItem {
 public:
     BeamWavelengthItem();
     void readFrom(QXmlStreamReader* r) override;
-    double wavelength() const;
 };
 
 #endif // BORNAGAIN_GUI_MODEL_BEAM_BEAMWAVELENGTHITEM_H

GUI/Model/Beam/SourceItems.cpp

@@ -94,7 +94,7 @@ void SourceItem::readFrom(QXmlStreamReader* r)
 double SourceItem::wavelength() const
 {
     ASSERT(m_wavelength_item);
-    return m_wavelength_item->wavelength();
+    return m_wavelength_item->meanValue();
 }
 
 void SourceItem::setWavelength(double value)