[nasdaq.nyse.day.trader]

I couldn't trade without it.
I use a combo of charts, then level 2 and T&S. There are several fakes the MMs play and that means that maybe 90% of the time they are of no real use.
However, 10% of the time level 2 and T&S tell you what is going to happen before a chart tells you anything. Sorting that 10% out is what makes level 2 and T&S priceless. You require the skills to read them or make intelligent guesses as to what is going on. I guess the nearest thing is reading the road ahead and anticipating when you're driving.