Update 4 6 time series data

4-6-time-series-data.md

@@ -57,6 +57,7 @@ In order to see the changes of the temperature over time, you can:
 ![](img/4-6-temperature-change-animation.gif)
 
 
+##### 6. Difference In Time (optional)
 
 In order to calculate and display the difference of temperature between the current time stamp and the previous time stamp, you can click the *Difference In Time* button in *Horizontal Plane* menu category of the **Menu Bar**.