diff --git a/mainwindow.ui b/mainwindow.ui
--- a/mainwindow.ui
+++ b/mainwindow.ui
@@ -322,6 +322,9 @@
               <height>16777215</height>
              </size>
             </property>
+            <property name="toolTip">
+             <string>lower limit of Y axis</string>
+            </property>
             <property name="value">
              <double>0.000000000000000</double>
             </property>
@@ -329,6 +332,9 @@
           </item>
           <item row="0" column="1">
            <widget class="QSpinBox" name="spNumOfSamples">
+            <property name="toolTip">
+             <string>length of X axis</string>
+            </property>
             <property name="keyboardTracking">
              <bool>false</bool>
             </property>
@@ -391,6 +397,9 @@
               <height>16777215</height>
              </size>
             </property>
+            <property name="toolTip">
+             <string>upper limit of Y axis</string>
+            </property>
             <property name="maximum">
              <double>1000.000000000000000</double>
             </property>