All they are is bids and asks being added & removed (depending if they are above or below the centre line).
Example: You see a bar appear on the right, above the line that lines up with $14.40 for the amount of 100BTC. You then see a red bar appear to the right appear below the line corresponding to $14.2 for the amount of - 10
This means someone placed an ask for $14.40 for 100BTC while someone removed an ask of $14.2 for 10BTC.
What is blowing my mind is that there are two many 'degrees of freedom'...at my current level of understanding of trading at least.
There are colors(red/green) and directions(up/down). The WTF link describes the colors, but not the direction as best I can determine.
The WTF link states that bids are on the left and asks are on the right. Period. Relax that and I could (possibly) see a solution.
Even with your example, I really don't see it (unless the interplay between several bid/ask's is a factor.)
How about this: Market at $14
- I see a green bar at 13.10 with a value of +10 (upward and on the left hence a bid added.)
- I see a green bar at 12.90 with a value of -12 (downward and on the left hence a bid added.)
What is the interpretation?