I am no expert, but from what I have read, there are several ways they do it. One way is to separate entries into groups and pick a group at random (i.e. like picking a numbered ball out of a hat) and then hand pick a winner out of that group. Like sticking your hand in and pulling one out. On the computer, they may push there finger down all the way, and where it stops, that is the winner. Like I said, I guess there are many ways to do it.