diff --git a/qthelper.cpp b/qthelper.cpp
index c51e13628..894601c80 100644
--- a/qthelper.cpp
+++ b/qthelper.cpp
@@ -48,7 +48,7 @@ bool DiveComputerNode::changesValues(const DiveComputerNode &b) const
 	       (nickName != b.nickName);
 }
 
-const DiveComputerNode *DiveComputerList::getExact(QString m, uint32_t d)
+const DiveComputerNode *DiveComputerList::getExact(const QString& m, uint32_t d)
 {
 	for (QMap<QString, DiveComputerNode>::iterator it = dcMap.find(m); it != dcMap.end() && it.key() == m; ++it)
 		if (it->deviceId == d)
@@ -56,7 +56,7 @@ const DiveComputerNode *DiveComputerList::getExact(QString m, uint32_t d)
 	return NULL;
 }
 
-const DiveComputerNode *DiveComputerList::get(QString m)
+const DiveComputerNode *DiveComputerList::get(const QString& m)
 {
 	QMap<QString, DiveComputerNode>::iterator it = dcMap.find(m);
 	if (it != dcMap.end())
@@ -64,7 +64,7 @@ const DiveComputerNode *DiveComputerList::get(QString m)
 	return NULL;
 }
 
-void DiveComputerList::addDC(QString m, uint32_t d, QString n, QString s, QString f)
+void DiveComputerList::addDC(const QString& m, uint32_t d, const QString& n, const QString& s,const QString& f)
 {
 	if (m.isEmpty() || d == 0)
 		return;
@@ -86,7 +86,7 @@ void DiveComputerList::addDC(QString m, uint32_t d, QString n, QString s, QStrin
 	dcMap.insert(m, newNode);
 }
 
-void DiveComputerList::rmDC(QString m, uint32_t d)
+void DiveComputerList::rmDC(const QString& m, uint32_t d)
 {
 	const DiveComputerNode *existNode = this->getExact(m, d);
 	dcMap.remove(m, *existNode);
diff --git a/qthelper.h b/qthelper.h
index 648a68090..9d31f5a12 100644
--- a/qthelper.h
+++ b/qthelper.h
@@ -29,12 +29,12 @@ class DiveComputerList {
 public:
 	DiveComputerList();
 	~DiveComputerList();
-	const DiveComputerNode *getExact(QString m, uint32_t d);
-	const DiveComputerNode *get(QString m);
-	void addDC(QString m, uint32_t d, QString n = "", QString s = "", QString f = "");
-	void rmDC(QString m, uint32_t d);
-	DiveComputerNode matchDC(QString m, uint32_t d);
-	DiveComputerNode matchModel(QString m);
+	const DiveComputerNode *getExact(const QString& m, uint32_t d);
+	const DiveComputerNode *get(const QString& m);
+	void addDC(const QString& m, uint32_t d,const QString& n = QString(),const QString& s = QString(), const QString& f = QString());
+	void rmDC(const QString& m, uint32_t d);
+	DiveComputerNode matchDC(const QString& m, uint32_t d);
+	DiveComputerNode matchModel(const QString& m);
 	QMultiMap<QString, DiveComputerNode> dcMap;
 	QMultiMap<QString, DiveComputerNode> dcWorkingMap;
 };