On the chart, price looks like one simple number — but behind it are streams from dozens of banks, aggregators, bridges and filters. We trace a tick's road from the market maker to the candle on your screen: why two brokers show different prices at the same moment, where ticks disappear, and where in this chain the arbitrage window lives.
Ask your terminal what the euro costs and it answers without hesitation. But that confident number has no single author: in forex there is no central exchange and no “official” price. What you see on the chart is the end of a long chain: banks and venues quote, aggregators collect, the broker adds its own touch, the feed thins the stream out. Let's walk the tick's whole road — from market maker to candle — and see where along the way the price manages to change, fall behind and diverge from its neighbors.
Forex is an over-the-counter (OTC) market: instead of one venue, a web of thousands of bilateral agreements. Prices are made by market makers — major banks and ECN venues like EBS: each constantly publishes its own two prices — the bid (what it will buy at) and the ask (what it will sell at). The gap between them, the spread, is the price of trading. There is no single price at any moment: there are dozens of opinions that usually almost agree — while the market is calm.
Then the funnel goes to work. The aggregator collects the providers' streams and at every moment picks the best bid and ask of them all. The broker takes that stream, adds its markup to the spread, pushes it through a bridge to the trading server — and only then does the price become “its” price, the one you see. Every step has its own milliseconds and its own rules.
A tick is not “once per second” — it's a fact: someone's best price changed. In a sleepy hour a pair sees dozens of ticks per minute; on a news release, hundreds per second. Candles are just packaging: a one-minute candle faithfully retells everything that arrived within the minute. The catch is the word “arrived”: a retail feed almost always throttles the stream — the terminal receives 2–10 updates per second, picked out of hundreds. The rest of the ticks simply don't exist for you.
And the tick travels the network. The road from the aggregator to your screen obeys the same physics we covered in the ping article: every intermediary and every kilometer adds milliseconds. By the time a price is drawn on the chart, it is already history — the only question is how old.
Now the main part. The same price has a fast road and a slow one. A fast feed takes quotes almost at the source — OnlyForex feed nodes run in London, New York and Tokyo, next to the places where price is born. The broker's retail feed travels longer: aggregation, the bridge, processing on the MT server, throttling. The difference between the two is tens, sometimes hundreds of milliseconds.
That difference is the arbitrage window: the engine sees on the fast feed that the world's price has already moved while the broker still shows the old quote — and places the order before the new price arrives. Nothing mystical: pure route geometry from our previous articles, applied to a stream of quotes.
While the tick traveled to you and your order traveled back, the market kept living. Execution happens at the server's price at the moment your order arrives, not at the picture on your chart. That's slippage — and it grows with the length of your route; see the ping article.
The server replies: “can't do that price anymore — here's a new one, agreed?” It's how a broker protects itself from filling at a stale quote. Frequent requotes in a fast market are a sign of a slow bridge or cautious execution settings.
Liquidity sleeps: provider banks scale back between sessions, the best bids and asks drift apart, and the aggregator simply has nothing to build a tight spread from. The same happens on news — only sharper.
It can: the feed belongs to the broker, and abuses do happen — up to candles being redrawn after you open a trade. More often, though, the differences have prosaic causes: other providers, markup, a slow bridge. The one real test is systematic comparison against an independent source; one-off differences prove nothing — but history that changes after the fact says a lot.
Dukascopy and TrueFX give away ticks for free — enough for most backtests. Remember: it's the history of their feeds, and you'll be trading on your broker's feed — budget for the divergence in advance.
Distance to the source and the absence of extra stations: no bridge, no MT-server processing, no throttling, protocols like FIX. The retail feed rides the whole conveyor and arrives tens to hundreds of milliseconds later — that difference is what latency arbitrage stands on.
The OnlyForex engine compares the broker's quotes with the fast stream from nodes in London, New York and Tokyo — and finds the moments when the broker's price has fallen behind. How to assemble the whole stack — from broker and VPS to the first trade — is laid out in the guide; the first chapters are open.