diff --git a/scalepicker.cpp b/scalepicker.cpp
new file mode 100644
--- /dev/null
+++ b/scalepicker.cpp
@@ -0,0 +1,250 @@
+/*
+  Copyright © 2015 Hasan Yavuz Özderya
+
+  This file is part of serialplot.
+
+  serialplot is free software: you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 3 of the License, or
+  (at your option) any later version.
+
+  serialplot is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with serialplot.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#include <QEvent>
+#include <QMouseEvent>
+#include <QPainter>
+#include <qwt_scale_widget.h>
+#include <qwt_scale_map.h>
+#include <math.h>
+
+#include "scalepicker.h"
+
+// minimum size for pick (in pixels)
+#define MIN_PICK_SIZE (2)
+
+class PlotOverlay : public QwtWidgetOverlay
+{
+public:
+    PlotOverlay(QWidget* widget, ScalePicker* picker);
+
+protected:
+    virtual void drawOverlay(QPainter*) const;
+
+private:
+    ScalePicker* _picker;
+};
+
+PlotOverlay::PlotOverlay(QWidget* widget, ScalePicker* picker) :
+    QwtWidgetOverlay(widget)
+{
+    _picker = picker;
+}
+
+void PlotOverlay::drawOverlay(QPainter* painter) const
+{
+    _picker->drawPlotOverlay(painter);
+}
+
+class ScaleOverlay : public QwtWidgetOverlay
+{
+public:
+    ScaleOverlay(QWidget* widget, ScalePicker* picker);
+
+protected:
+    virtual void drawOverlay(QPainter*) const;
+
+private:
+    ScalePicker* _picker;
+};
+
+ScaleOverlay::ScaleOverlay(QWidget* widget, ScalePicker* picker) :
+    QwtWidgetOverlay(widget)
+{
+    _picker = picker;
+}
+
+void ScaleOverlay::drawOverlay(QPainter* painter) const
+{
+    _picker->drawScaleOverlay(painter);
+}
+
+ScalePicker::ScalePicker(QwtScaleWidget* scaleWidget, QWidget* canvas) :
+    QObject(scaleWidget)
+{
+    _scaleWidget = scaleWidget;
+    _canvas = canvas;
+    scaleWidget->installEventFilter(this);
+    scaleWidget->setMouseTracking(true);
+    pickerOverlay = new PlotOverlay(canvas, this);
+    scaleOverlay = new ScaleOverlay(scaleWidget, this);
+    started = false;
+    pressed = false;
+}
+
+bool ScalePicker::eventFilter(QObject* object, QEvent* event)
+{
+    if (event->type() == QEvent::MouseButtonPress ||
+        event->type() == QEvent::MouseButtonRelease ||
+        event->type() == QEvent::MouseMove)
+    {
+        QMouseEvent* mouseEvent = (QMouseEvent*) event;
+        double pos = this->position(mouseEvent);
+        double posPx = this->positionPx(mouseEvent);
+        currentPosPx = posPx;
+
+        if (event->type() == QEvent::MouseButtonPress &&
+            mouseEvent->button() == Qt::LeftButton)
+        {
+            pressed = true; // not yet started
+            firstPos = pos;
+            firstPosPx = posPx;
+        }
+        else if (event->type() == QEvent::MouseMove)
+        {
+            // make sure pick size is big enough, so that just
+            // clicking won't trigger pick
+            if (!started && pressed && (fabs(posPx-firstPosPx) > MIN_PICK_SIZE))
+            {
+                started = true;
+                emit pickStarted(pos);
+            }
+            else if (started)
+            {
+                pickerOverlay->updateOverlay();
+                emit picking(firstPos, pos);
+            }
+            scaleOverlay->updateOverlay();
+        }
+        else // event->type() == QEvent::MouseButtonRelease
+        {
+            if (started)
+            {
+                // finalize
+                started = false;
+                pressed = false;
+                emit picked(firstPos, pos);
+            }
+        }
+        return true;
+    }
+    else if (event->type() == QEvent::Leave)
+    {
+        scaleOverlay->updateOverlay();
+        return true;
+    }
+    else
+    {
+        return QObject::eventFilter(object, event);
+    }
+}
+
+void ScalePicker::drawPlotOverlay(QPainter* painter)
+{
+    if (started)
+    {
+        painter->save();
+        painter->setPen(_pen);
+
+        QRect rect;
+        if (_scaleWidget->alignment() == QwtScaleDraw::BottomScale ||
+            _scaleWidget->alignment() == QwtScaleDraw::TopScale)
+        {
+            int height = painter->device()->height();
+            rect = QRect(posCanvasPx(firstPosPx), 0, currentPosPx-firstPosPx, height);
+        }
+        else // vertical
+        {
+            int width = painter->device()->width();
+            rect = QRect(0, posCanvasPx(firstPosPx), width, currentPosPx-firstPosPx);
+        }
+        painter->drawRect(rect);
+        painter->restore();
+    }
+}
+
+void ScalePicker::drawScaleOverlay(QPainter* painter)
+{
+    painter->save();
+    painter->setPen(_pen);
+    if (1)
+    {
+
+        if (_scaleWidget->alignment() == QwtScaleDraw::BottomScale ||
+            _scaleWidget->alignment() == QwtScaleDraw::TopScale)
+        {
+            int height = painter->device()->height();
+            if (started) painter->drawLine(firstPosPx, 0, firstPosPx, height);
+            if (started || _scaleWidget->underMouse())
+            {
+                painter->drawLine(currentPosPx, 0, currentPosPx, height);
+            }
+        }
+        else // vertical
+        {
+            int width = painter->device()->width();
+            if (started) painter->drawLine(0, firstPosPx, width, firstPosPx);
+            if (started || _scaleWidget->underMouse())
+            {
+                painter->drawLine(0, currentPosPx, width, currentPosPx);
+            }
+        }
+    }
+    painter->restore();
+}
+
+void ScalePicker::setPen(QPen pen)
+{
+    _pen = pen;
+}
+
+double ScalePicker::position(QMouseEvent* mouseEvent)
+{
+    double pos;
+    pos = positionPx(mouseEvent);
+    // convert the position of the click to the plot coordinates
+    pos = _scaleWidget->scaleDraw()->scaleMap().invTransform(pos);
+    return pos;
+}
+
+double ScalePicker::positionPx(QMouseEvent* mouseEvent)
+{
+    double pos;
+    if (_scaleWidget->alignment() == QwtScaleDraw::BottomScale ||
+        _scaleWidget->alignment() == QwtScaleDraw::TopScale)
+    {
+        pos = mouseEvent->pos().x();
+    }
+    else // left or right scale
+    {
+        pos = mouseEvent->pos().y();
+    }
+    return pos;
+}
+
+/*
+ * Scale widget and canvas widget is not always aligned. Especially
+ * when zooming scaleWidget moves around. This causes irregularities
+ * when drawing the tracker lines. This function maps scale widgets
+ * pixel coordinate to canvas' coordinate.
+ */
+double ScalePicker::posCanvasPx(double pos)
+{
+    // assumption: scale.width < canvas.width && scale.x > canvas.x
+    if (_scaleWidget->alignment() == QwtScaleDraw::BottomScale ||
+        _scaleWidget->alignment() == QwtScaleDraw::TopScale)
+    {
+        return pos + (_scaleWidget->x() - _canvas->x());
+    }
+    else // left or right scale
+    {
+        return pos + (_scaleWidget->y() - _canvas->y());
+    }
+    return pos;
+}