I'd like listen to your comment on how exactly the quote tick moves. I suggest there must be many kinds of motion of tick with different causes. I would shrug on a general statement saying it is simply all because of demand and supply. I noticed there were wonderful threads about tape reading. I like to extend the topic with concrete examples in discussion. Let me start with an example which is the motion drive by normal demand and supply. For simplicity, let's make the assumption that there is only one exchange. Okay, let's roll the tape. Time Bid Size(100) Ask T+0: P+0 10x10 P+10 T+1: P+5 1 x10 P+10 T+2: P+5 6 x5 P+10 T+3: Trade 1@P+10 T+3: P+5 5 x 4 P+10 T+4: P+8 5 x 4 P+10 In this simple case, the outside buyers drive the tick&last price up given the fact that the market make do not insist to hold the offer. I know there must be many cases and interpretations in the real-world. But let's start with simplified cases to understand the ticks. Please present your favorite examples, either simplified from your memorable trades or watch, or a hypothetical one. Thanks. And similar academic or nonacademic references on the topic are welcome. Thanks.