Using Arduino UNO board and servo motor to make the arm point in one direction.

Hello everybody. My project is about making a tracking device that makes servo motor point in one direction. here is a small demo of it. I am not able to spot how he did this. So please help me.... URGENT. it is a part of my Graduation Farewell Science fair. Please help me out.

https://www.youtube.com/watch?v=1gOCKOwCeQ4

If it is URGENT I suggest you find another project. That one won't be simple.

...R