diff --git a/src/zoomer.cpp b/src/zoomer.cpp
--- a/src/zoomer.cpp
+++ b/src/zoomer.cpp
@@ -29,11 +29,6 @@ Zoomer::Zoomer(QWidget* widget, bool doR
 
 void Zoomer::zoom(int up)
 {
-    if (up == +1)
-    {
-        this->setZoomBase(this->plot());
-    }
-
     ScrollZoomer::zoom(up);
 
     if(zoomRectIndex() == 0)
@@ -41,3 +36,14 @@ void Zoomer::zoom(int up)
         emit unzoomed();
     }
 }
+
+void Zoomer::zoom( const QRectF & rect)
+{
+    // set the zoom base when user zooms in to first level
+    if (zoomRectIndex() == 0)
+    {
+        this->setZoomBase(false);
+    }
+
+    ScrollZoomer::zoom(rect);
+}
diff --git a/src/zoomer.h b/src/zoomer.h
--- a/src/zoomer.h
+++ b/src/zoomer.h
@@ -29,6 +29,7 @@ class Zoomer : public ScrollZoomer
 public:
     Zoomer(QWidget *, bool doReplot=true);
     void zoom(int up);
+    void zoom( const QRectF & );
 
 signals:
     void unzoomed();