diff --git a/gtk2_ardour/automation_line.cc b/gtk2_ardour/automation_line.cc
index 120fa176a8e..ca66fe8fb85 100644
--- a/gtk2_ardour/automation_line.cc
+++ b/gtk2_ardour/automation_line.cc
@@ -394,26 +394,58 @@ AutomationLine::delta_to_string (double delta) const
  *  @return Corresponding y fraction.
  */
 double
-AutomationLine::string_to_fraction (string const & s) const
+AutomationLine::string_to_fraction (string const & s, double const old_fraction) const
 {
-	double v;
-	sscanf (s.c_str(), "%lf", &v);
-
+	bool is_db = false;
 	switch (_desc.type) {
 		case GainAutomation:
 		case BusSendLevel:
 		case EnvelopeAutomation:
 		case TrimAutomation:
 		case InsertReturnLevel:
-			if (s == "-inf") { /* translation */
-				v = 0;
-			} else {
-				v = dB_to_coefficient (v);
-			}
+			is_db = true;
 			break;
 		default:
 			break;
 	}
+	double v;
+	if ((s.length() > 2) && index("+-*/", s[0]) && (s[1] == '=')) {
+		v = old_fraction;
+		view_to_model_coord_y (v);
+		if (is_db) {
+			v = accurate_coefficient_to_dB(v);
+		}
+		double op_v;
+		sscanf (s.c_str() + 2, "%lf", &op_v);
+		if (op_v != 0.f) {
+			switch (s[0]) {
+				case '+':
+					v += op_v;
+					break;
+				case '-':
+					v -= op_v;
+					break;
+				case '*':
+					v *= op_v;
+					break;
+				case '/':
+					if (op_v > 1.0) {
+						v /= op_v;
+					}
+					break;
+			}
+		}
+	} else {
+		sscanf (s.c_str(), "%lf", &v);
+	}
+
+	if (is_db) {
+		if (s == "-inf") { /* translation */
+			v = 0;
+		} else {
+			v = dB_to_coefficient (v);
+		}
+	}
 	return model_to_view_coord_y (v);
 }
 
diff --git a/gtk2_ardour/automation_line.h b/gtk2_ardour/automation_line.h
index 8c3ca154c58..553c0fc5823 100644
--- a/gtk2_ardour/automation_line.h
+++ b/gtk2_ardour/automation_line.h
@@ -125,7 +125,7 @@ class AutomationLine : public sigc::trackable, public PBD::StatefulDestructible
 	std::string get_verbose_cursor_relative_string (double, double) const;
 	std::string fraction_to_string (double) const;
 	std::string delta_to_string (double) const;
-	double string_to_fraction (std::string const &) const;
+	double string_to_fraction (std::string const &, double old_fraction) const;
 
 	void   view_to_model_coord_y (double &) const;
 
diff --git a/gtk2_ardour/control_point_dialog.cc b/gtk2_ardour/control_point_dialog.cc
index ac82cfd0762..a49d0bb0cda 100644
--- a/gtk2_ardour/control_point_dialog.cc
+++ b/gtk2_ardour/control_point_dialog.cc
@@ -90,9 +90,11 @@ ControlPointDialog::ControlPointDialog (ControlPoint* p, bool multi)
 }
 
 double
-ControlPointDialog::get_y_fraction () const
+ControlPointDialog::get_y_fraction (ControlPoint* p) const
 {
-	return point_->line().string_to_fraction (value_.get_text ());
+	double const old_fraction = 1.0 - (p->get_y () / p->line().height ());
+
+	return point_->line().string_to_fraction (value_.get_text (), old_fraction);
 }
 
 bool
diff --git a/gtk2_ardour/control_point_dialog.h b/gtk2_ardour/control_point_dialog.h
index c0ef2627cbf..73961ae8dbb 100644
--- a/gtk2_ardour/control_point_dialog.h
+++ b/gtk2_ardour/control_point_dialog.h
@@ -29,7 +29,7 @@ class ControlPointDialog : public ArdourDialog
 public:
 	ControlPointDialog (ControlPoint *, bool multi);
 
-	double get_y_fraction () const;
+	double get_y_fraction (ControlPoint *) const;
 
 	bool all_selected_points () const;
 
diff --git a/gtk2_ardour/editor_mouse.cc b/gtk2_ardour/editor_mouse.cc
index 40af6606286..6141e1c8b4c 100644
--- a/gtk2_ardour/editor_mouse.cc
+++ b/gtk2_ardour/editor_mouse.cc
@@ -2514,11 +2514,11 @@ Editor::edit_control_point (ArdourCanvas::Item* item)
 	}
 
 	if (d.all_selected_points ()) {
-		p->line().modify_points_y (cps, d.get_y_fraction ());
+		p->line().modify_points_y (cps, d.get_y_fraction (p)); // FIXME: multi edit somehow?
 	} else {
 		cps.clear ();
 		cps.push_back (p);
-		p->line().modify_points_y (cps, d.get_y_fraction ());
+		p->line().modify_points_y (cps, d.get_y_fraction (p));
 	}
 }