What did I see come through Farringdon this afternoon, heading westbound maybe around 13.50hrs? It looked like it used to be Piccadilly stock (I say that because it had Piccadilly Line on the side!) but was fitted out inside with desks and maybe computer terminals (I think but I am pretty tired). I've never seen it before but i'm guessing it's some sort of monitoring train? Ideas anyone? Or am I just going mad...