Listen to the following riddle and see if you can solve it: There are 3 light bulbs in three separate rooms. in front of you, there is a panel with 3 separate switches. They only turn on or off. You may look inside each room only once. How can you tell which bulb belongs to which switch?
The answer would be that we can't as one bulb could correspond to two switches. A solution however exists if you use timestamps. Each time the lights change state, you write down whether they turned on, off or did not affect anything when you were last looking into the corresponding room (you do this by starting at the end that was affected).
Then read from top right corner clockwise until all columns have been seen at least once. Whichever column has the latest timestamp will therefore contain information about the current status of the third (and final) switch: Which one didn't move, indicating that's what was controlling both other bulbs respectively - meaning their counterpart switched them off too.