Reading bid/ask delta inside a TPO profile

Time at price and bid/ask volume are two different questions; putting the delta inside each TPO letter answers both in one view.

A TPO profile answers one question: where did the session spend its time? A delta reading answers a different one: of the volume that traded, how much of it lifted offers and how much hit bids? Neither answer contains the other. A price can hold the most time in the session and be almost perfectly balanced on delta, and a price the market touched for a single period can carry the largest one-sided volume of the day. Keeping both in the same view means not switching between two charts to compare them.

What a TPO letter is

A TPO — a time price opportunity — is one mark for one time period at one price. The session is divided into equal periods, thirty minutes being the usual choice; each period gets a letter, and that letter is printed at every price the market traded during it. The periods stack left to right and the letters pile up into the profile shape.

The count of letters in a row is therefore a count of periods, not of contracts. A row with twelve letters is a price that traded in twelve separate periods. The point of control is the row holding the most letters: the price with the most time. It is not the price with the most volume — that is the volume point of control, chosen by a different measure and not necessarily the same row. The value area is built the same way, expanded out from the point of control until it covers a set share of the session's total letter count, seventy percent by convention.

Everything in that paragraph is a statement about time. Not one of those numbers knows how many contracts traded, or on which side.

What delta is

Delta is ask-traded volume minus bid-traded volume. Each trade is compared against the bid and ask quoted at the moment it printed: at or above the ask it counts as a buy, at or below the bid it counts as a sell. Trades between the two are ambiguous and have to be handled by rule — comparing against the last classified trade is one common approach, where a higher price counts as a buy and a lower one as a sell, and an unchanged price contributes nothing to delta while its volume still counts.

Aggregated over a period at a price, that leaves a number with a sign. Positive means more volume came in at the ask than at the bid over that period at that price; negative means the reverse. The magnitude is a net contract count, not a total — a delta of 400 at a price that traded 500 contracts and a delta of 400 at a price that traded 20,000 are not the same reading, and only the volume figure alongside it separates them.

Reading them together

With the delta on the letter, each cell carries two independent facts: this period visited this price, and this is what the classified volume did while it was here.

A few combinations, described and nothing more. A row deep in the value area with many letters and a delta near zero is time spent with classified buy and sell volume roughly matched. The same row with many letters and a large one-sided delta is the same amount of time with the volume unbalanced. A single letter at the extreme top of the profile carrying a large negative delta records one period at that price in which sell-classified volume dominated the trades that printed there, and the row below it may carry a positive delta in the same period.

Across a row, the balance at one price is legible period by period. Down a period's column, the prices where that period's volume ran one-sided are legible against the ones where it did not. Neither reading is a conclusion. They are two measurements of the same session placed side by side, and nothing in the profile combines them into a third.

Where this shows up in my own tools

TakeFlight TPO is the market profile I built to put the delta inside the profile itself rather than in a pane underneath it: every TPO letter carries its own bid/ask volume delta, the classification runs off a one-tick series the indicator adds itself so no Tick Replay is involved, and the session point of control, value area and initial balance are drawn alongside a per-row volume and delta column.

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