Rebel GII light meter ?

I'm used to light meters with a + or - or a red and green dot that indicate the lighting. I just bought an open box GII that has no instruction manual. What is the light meter and how do I read it?

I'm assuming it's the 3 green bars in line. But how do I read those 3 bars. I assume when the one to the left is lit then too little light. When the bar to the right is lit then too much light. But when is it just right? When just the middle bar is lit or when all 3 are lit?

Also, this instruction manual is not available online, and I figured everything else out except the light meter.

Thanks.

Ok, I figured out the light meter by looking at a Rebel Ti instruction manual online. It is the -2 -1 0 1 2

But what are the 3 bars? I assume they somehow correspond to the 3 bars used for setting up the 3rds of the photo and deciding what is in focus. But why are all 3 sometimes lit, then 1 lit then 2 then the other 2? What exactly is going on there?

Thanks.