diff --git a/src/main/java/org/solovyev/android/calculator/CalculatorActivity.java b/src/main/java/org/solovyev/android/calculator/CalculatorActivity.java
index 88cf20e0..99deefe5 100644
--- a/src/main/java/org/solovyev/android/calculator/CalculatorActivity.java
+++ b/src/main/java/org/solovyev/android/calculator/CalculatorActivity.java
@@ -37,6 +37,9 @@ public class CalculatorActivity extends Activity implements FontSizeAdjuster {
 	@NotNull
 	private CalculatorModel calculator;
 
+	@NotNull
+	private BroadcastReceiver preferencesChangesReceiver;
+
 	/**
 	 * Called when the activity is first created.
 	 */
@@ -112,7 +115,7 @@ public class CalculatorActivity extends Activity implements FontSizeAdjuster {
 		onDragListeners.add(toPositionOnDragListener);
 
 
-		final BroadcastReceiver preferencesChangesReceiver = new BroadcastReceiver() {
+		preferencesChangesReceiver = new BroadcastReceiver() {
 			@Override
 			public void onReceive(Context context, Intent intent) {
 
@@ -128,6 +131,12 @@ public class CalculatorActivity extends Activity implements FontSizeAdjuster {
 		registerReceiver(preferencesChangesReceiver, new IntentFilter(DragButtonCalibrationActivity.INTENT_ACTION));
 	}
 
+	@Override
+	protected void onDestroy() {
+		unregisterReceiver(preferencesChangesReceiver);
+		super.onDestroy();
+	}
+
 	@SuppressWarnings({"UnusedDeclaration"})
 	public void elementaryButtonClickHandler(@NotNull View v) {
 		throw new UnsupportedOperationException("Not implemented yet!");
diff --git a/src/main/java/org/solovyev/android/calculator/CalculatorView.java b/src/main/java/org/solovyev/android/calculator/CalculatorView.java
index 7344eec5..314016bb 100644
--- a/src/main/java/org/solovyev/android/calculator/CalculatorView.java
+++ b/src/main/java/org/solovyev/android/calculator/CalculatorView.java
@@ -2,6 +2,7 @@ package org.solovyev.android.calculator;
 
 import android.app.Activity;
 import android.content.Context;
+import android.os.Handler;
 import android.text.ClipboardManager;
 import android.text.InputType;
 import android.view.View;
@@ -15,6 +16,8 @@ import org.jetbrains.annotations.Nullable;
 import org.solovyev.util.StringUtils;
 import org.solovyev.util.math.MathEntityType;
 
+import java.util.Date;
+
 /**
  * User: serso
  * Date: 9/12/11
@@ -96,19 +99,31 @@ public class CalculatorView implements CursorControl{
 
 		final String editorStateAfter = this.editor.getText().toString();
 		if (!editorStateBefore.equals(editorStateAfter)) {
-			try {
-				evaluate(editorStateAfter);
-			} catch (EvalError evalError) {
-				// actually nothing shall be logged while text operations are done
-			}
+			// actually nothing shall be logged while text operations are done
+			evaluate(editorStateAfter, false);
 
 			saveHistoryState();
 		}
 	}
 
-	private void evaluate(@Nullable String expression) throws EvalError {
+	private void evaluate(@Nullable final String expression, final boolean showError) {
 		if (!StringUtils.isEmpty(expression)) {
-			display.setText(calculator.evaluate(JsclOperation.numeric, expression));
+
+			final TextView localDisplay = display;
+			final Activity localActivity = activity;
+
+			new Handler().post(new Runnable() {
+				@Override
+				public void run() {
+					try {
+						localDisplay.setText(calculator.evaluate(JsclOperation.numeric, expression));
+					} catch (EvalError evalError) {
+						if (showError) {
+							Toast.makeText(localActivity, R.string.syntax_error, Toast.LENGTH_SHORT).show();
+						}
+					}
+				}
+			});
 		}
 	}
 
@@ -121,11 +136,7 @@ public class CalculatorView implements CursorControl{
 	}
 
 	public void evaluate() {
-		try {
-			evaluate(editor.getText().toString());
-		} catch (EvalError evalError) {
-			Toast.makeText(this.activity, R.string.syntax_error, Toast.LENGTH_SHORT).show();
-		}
+		evaluate(editor.getText().toString(), true);
 	}
 
 	public void processButtonAction(@Nullable final String text) {
diff --git a/src/main/java/org/solovyev/android/calculator/DragButtonCalibrationActivity.java b/src/main/java/org/solovyev/android/calculator/DragButtonCalibrationActivity.java
index a2efa2b2..35edec09 100644
--- a/src/main/java/org/solovyev/android/calculator/DragButtonCalibrationActivity.java
+++ b/src/main/java/org/solovyev/android/calculator/DragButtonCalibrationActivity.java
@@ -216,12 +216,12 @@ public class DragButtonCalibrationActivity extends Activity {
 						}
 						break;
 					case distance:
-						defaultMin = 60f;
-						defaultMax = 140f;
+						defaultMin = 50f;
+						defaultMax = 150f;
 						break;
 					case duration:
-						defaultMin = 100f;
-						defaultMax = 300f;
+						defaultMin = 40f;
+						defaultMax = 1000f;
 						break;
 					default:
 						defaultMin = DEFAULT_VALUE;
diff --git a/src/main/java/org/solovyev/android/view/DragButton.java b/src/main/java/org/solovyev/android/view/DragButton.java
index f1347fe3..282e9c92 100644
--- a/src/main/java/org/solovyev/android/view/DragButton.java
+++ b/src/main/java/org/solovyev/android/view/DragButton.java
@@ -1,5 +1,7 @@
 package org.solovyev.android.view;
 
+import android.os.Handler;
+import android.widget.Button;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 import org.solovyev.util.math.Point2d;
@@ -76,6 +78,19 @@ public class DragButton extends ColorButton {
 								// prevent on click action
 								setPressed(false);
 							}
+
+
+							if (v instanceof Button) {
+								final Button button = (Button)v;
+
+								button.setEnabled(false);
+
+								new Handler().postDelayed(new Runnable() {
+									public void run() {
+										button.setEnabled(true);
+									}
+								}, 500);
+							}
 						}
 
 						startPoint = null;
diff --git a/src/misc/stats.ods b/src/misc/stats.ods
new file mode 100644
index 00000000..42771d33
Binary files /dev/null and b/src/misc/stats.ods differ