Must be getting on 20 years ago... I was the Air controller at Heathrow one evening when the boss brought up a charming young lady for a look around.... asked if she could listen in with me, etc. She asked me things like: "How you you know which plane you are talking to", "How can you tell the difference between the planes", etc, etc. I tried to give her basic answers which I hoped she might understand. Boss came across and whispered in my ear: "She's just finished at the College and starts in Glasgow Tower in a few days". O....M...G!