Market replay and the sim account

Monday 9 November 2026, 08:00 ET (20:00 ICT). On Thursday 5 November the first fifteen minutes after the 09:30 ET open (21:30 ICT) took NQ from 28,228.25 down to 27,700.00: 528 points, about $1,056 on one micro contract. Could your hands have kept up? Would your stop have been where you planned it?

You can find out tonight without risking a dollar. This lesson shows how to replay that session in ATAS X, trade it on a practice account, and be honest about what practice fills cannot tell you.

Key terms

Market replay (phát lại thị trường): ATAS X plays a past session back tick by tick, so charts, footprint and order book behave as if that day were live Definition.

Replay account (tài khoản replay): the practice account ATAS X uses while replay is on. In the installed build it is named Replay and starts with a default balance of 100,000 Definition.

Sim account (tài khoản mô phỏng): an account that fills your orders against live prices with no money at risk. Your broker, data vendor or prop firm provides it, not the replay player Definition.

Fill (khớp lệnh): the price at which your order executed; on a practice account, software computes it Definition.

Blind pick (chọn mù): choosing which session to replay before you have seen how it went House rule.

Terms you need: MNQ and bracket. MNQ is the micro Nasdaq-100 future: one-tenth of NQ, $2 per point, $0.50 per 0.25-point tick (MKT1). A bracket is a stop and a target attached to your entry; when one fills, the other is cancelled (MKT2.06, PLAT2.07).

Chart first: one practice loop

What to see: the result of the trade is the least important box. The gates are what make a replay session count: picked blind, plan locked before play, every fill checked against the tape.

How it works

Two practice tools, two different jobs

While replay is on, ATAS X turns off all trading connections; orders go to the Replay account only Definition. You cannot send a live order from a replay chart. The reverse is not true: ATAS X marks only its own Replay account, and in our reading of the platform a broker’s sim account and a live account can look the same on screen. Read the account name before every order House rule.

Three replay data modes

The installed build offers three kinds of replay data Definition:

1. Candles (with generated best prices): bars only; the bid and ask are made up from the bars.
2. Ticks (with generated best prices): every real trade, but the order book is made up.
3. Ticks and DOM (Level 2): real trades and the real order book.

For order-flow practice use Ticks and DOM. In the two generated modes the depth on your DOM is software, not the market.

How much history you can play depends on your licence. The platform’s own messages list one instrument and one week of history in demo mode, one instrument and one day after a demo expires, and five instruments and three months on an extended demo Definition. ATAS help states that dxFeed instruments are not supported in Market Replay, so you need a feed such as Rithmic (PLAT2.01). Check the help center for your tier.

What replay cannot show you

• Your orders do not move the replayed prices. At one micro this matters little; at size it matters.
• Queue position is a guess. Live, a resting limit order waits behind everyone who was there first. ATAS does not document how its replay decides when you reach the front (our lab searched on 8 November 2026). Count a limit fill only when price trades through your price by at least one tick House rule.
• Nothing is at stake. Whether replay practice carries over to live results is not yet measured.
• A paused replay is silent. While paused, indicators receive no ticks or depth Definition. Silence is not a disconnect.

What the data says

Worked example: replaying Thursday 5 November 2026

All prices are real NQ ticks from our lab’s recorder (December 2026 contract). MNQ trades at the same prices as NQ.

1. Pick blind. Write five recent dates on paper and roll a die before opening any chart. It lands on Thursday 5 November, still inside a demo licence’s one-week window on Monday the 9th.
2. Load. Ticks and DOM mode, NQ December contract, start 09:15 ET (21:15 ICT). From 09:25, play at normal speed.
3. Lock the plan before play. To practise mechanics, not to test an idea: at 10:00 ET sell 1 MNQ at market, stop 60 points above, target 120 below; one trade only. Risk: 60 × $2 = $120.
4. Watch the open. The first trade prints 28,203.25; by 09:44:40 ET price is at 27,700.00. Note what that speed does to your hands.
5. Enter. At 10:00:00 ET the first trades print near 27,535.00. Bracket: stop 27,595.00, target 27,415.00.
6. Manage nothing. The highest price before the exit is 27,587.75, 7.25 points short of the stop. At 10:05:45 ET price touches 27,415.00; half a second later it trades 27,414.75, through your target. Count the fill: +120 points, +$240 before fees.
7. Journal row. Date, mode, plan, both fills, the tape price at each fill, “rule kept: yes”, and one line on your hands at 09:30.

The mirror and the failure

Mirror. Same plan, long side: buy near 27,535.00, stop 27,475.00, target 27,655.00. The stop trades at 10:01:22 ET: −60 points, −$120. The tape printed every tick down through 27,475 with no gap, so a live stop fill would probably have been close (not measured). In your journal this row is as good as the winner: plan written first, plan followed.

Failure. Suppose you chose 5 November because you remembered the sell-off. The winning short now tells you nothing; you knew the ending before you pressed play. Hand-picked days turn replay into a highlights reel.

Do it on the platform

Prop-firm note. Topstep’s evaluation and practice accounts are simulated, and the firm’s rules forbid exploiting simulated fills (PROP1.04). We have not yet written a dated rule card for this lesson, so read the help center’s prohibited-conduct article before you trade a firm account. MKT2.03 covers how sim fills differ from live ones.

Common mistake

Common mistake: Treating a practice P&L as proof of an edge. Three green weeks in replay measure a small sample of optimistic fills on days you may have recognised. Count your rule-kept rate and the number of trades first (EV2.04); your P&L only starts to mean something on live micros.

Drill: one blind replay session

1. Write five dates from the last week on paper. Roll a die or draw one without opening any chart.
2. Write your plan: time, side, size (1 MNQ), stop and target in points, one trade.
3. Replay from 15 minutes before the plan’s time in Ticks and DOM mode, at normal speed.
4. Place the bracket on the Replay account; touch nothing until it exits.
5. Log: fill prices, the tape price at each fill, whether a limit was traded through or only touched, rule kept yes/no.

What we don’t know yet

• How ATAS X replay decides when a resting limit order fills: not documented, not yet measured.
• How far replay or sim fills differ from live fills on NQ and MNQ: not yet measured on this desk (MKT2.03).
• Whether replay practice improves live results: not yet measured.

Recap

• Replay plays a past session on the Replay account; a sim account trades live prices. While replay runs, ATAS X turns off all trading connections.
• Use Ticks and DOM mode for order-flow practice; the other two modes generate the order book.
• Practice fills are likely optimistic: count a limit fill only when price traded through it.
• A replay session counts only if it was picked blind and the plan was written before play.

Further reading

• CME Group, Micro E-mini Nasdaq-100 contract specifications, cmegroup.com: point value and tick size of MNQ.
• Databento, “Getting queue position from L2 and order book data”, databento.com: why queue estimates from Level 2 data are optimistic.
• ATAS help center, help.atas.net: the Market Replay article lists the current history limits for each licence.
• Our lab: a review of how public backtest engines model fills, queues and latency, and why each says to check simulated fills against live ones.
• Our lab: recorded NQ ticks for Thursday 5 November 2026, used in the worked example.

Prerequisites: M0.07 Choosing software & data, M0.09 Reading a price chart · Next: PLAT2.07 Hotkeys, ATM bracket templates and flatten-all. You just placed a bracket by hand; the next lesson turns it into a one-click template and tests flatten-all on the Replay account.

Educational content only. Not financial advice. Futures trading involves substantial risk of loss.