Depth of Market: The Ladder, and Its Limits
Depth of market is a vertical ladder display of resting limit orders at each price, used mainly in futures where a single exchange holds the complete book. Its main advantage over a chart is execution speed rather than any information the book does not already contain.
How it works
Prices run vertically down the middle of the screen. Resting buy orders sit in a column on one side, sell orders on the other, with the size at each price shown beside it. Clicking a cell places an order at that price.
It is the same data as Level 2, presented for speed. The vertical layout puts every price within one click, which is why it became the standard interface for futures trading.
And the futures market structure is what makes it more meaningful than the equity equivalent. A given contract trades on one exchange. The book you see is the book — not one venue’s slice of a fragmented market with dark pools alongside it.
What it does and does not add
The ladder contains no data a Level 2 display lacks. Its contribution is interface: one-click entry, one-click exit, orders visibly attached to price levels, and no dialog boxes between an intention and an order.
For someone trading in seconds, that is a genuine and substantial advantage. For anyone holding positions for hours or days, it is a faster way to do something that was never the bottleneck.
In an active market the numbers change faster than they can be read. What a person actually perceives is an impression of activity, not a sequence of states — which is worth being honest about before building a method on “reading the ladder.”
Posting size with no intention of trading it is spoofing. It is illegal in most major jurisdictions and it has been prosecuted repeatedly, which is itself the evidence that it happens.
The practical consequence is that displayed size is not a commitment. A large resting order can be genuine, or it can be there to influence what you do, and the display cannot tell you which.
In practice
Most ladders show a traded-volume column alongside the resting orders. That column is the more reliable half of the display: executions cannot be cancelled, and order flow analysis is built on them for that reason.
Stops never appear. They are held at the broker or in a server-side queue and arrive as market orders when triggered — which is why a burst of activity can appear at a price with nothing showing there beforehand.
The information decays in seconds. Nothing in a ladder informs a decision about tomorrow, and the temptation to watch it while holding a longer-term position is a pure attention cost.
At the session break the ladder empties, and the thin book that remains is not representative of anything. The same applies in the first seconds after an opening gap.
Every click is a round trip: 2% of a median bar’s range on this site’s shared history, plus exchange and clearing fees on futures.
And on the smallest bar in the series that cost is 45% of the range. An interface built for speed makes it easy to trade often, and trading often on small bars is where a fixed cost does the most damage.
What depth of market is not
It is not extra data. It is Level 2 in a different layout, on a market where the book is complete.
It is not a display of stops. Nothing shows them.
It is not a commitment from other participants. Orders can be pulled, and some are posted in order to be seen.
And it is not useful without speed. Its advantage is the click; without a method that needs the click, there is no advantage.
When it fails
In a range the ladder is at its most active and least informative. Size builds and clears on both sides continuously, and every apparent imbalance is reversed within seconds.
The second failure is the human reading rate. In fast conditions the display outruns perception, and what feels like reading is pattern-matching on an impression.
A third is acting on displayed walls. They can be genuine, they can be icebergs showing a fraction, and they can be there to be seen. Three possibilities, one appearance.
A fourth is the over-trading the interface invites. One click to enter and one to exit removes the friction that was quietly limiting trade count, and the round-trip cost does not go away.
And a fifth is using it on a fragmented market. On equities the ladder shows one venue, which makes every imbalance reading partial.
The original data
On this site’s shared 576-bar history the round-trip cost is 0.0098 price units — 2% of the median bar
range of 0.493, 45% of the smallest bar of 0.022, and more than 10% of the bar’s range on 15 of the 576
bars — with ranges spanning 0.17 to 1.10 between the tenth and ninetieth percentiles. The figures are in
research/series-measurements.json, produced by site/measure_series.py.
That 15-bar figure is the honest test for whether a ladder belongs on your screen. Those are the bars where execution cost exceeds a tenth of everything the bar offered — and a fast interface makes it easy to trade exactly those bars, repeatedly, because there is always something happening on the display. Before subscribing, compute your round trip as a share of the moves you actually target; if the number is large, the ladder will help you make that mistake faster rather than help you avoid it.
Related
Order book is what the ladder is displaying and what it omits. Level 2 is the equity equivalent, on a fragmented market. And futures covers the market structure that makes the book complete.
The ladder is the only interface I have used where I could feel my own reaction time being the constraint. That is useful information about what kind of trading is available to a person clicking a mouse, and it is not the information the display was sold to me as providing.
— Michael Whitman
This page is educational, not financial advice. Test every idea on your own charts before risking money.