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DAS Replay
Updated

What's real and what's simulated

Every price is real history. Only your orders — and how they fill — are simulated.

Think of the desk as a flight simulator built from real black-box recordings. The weather, the turbulence, the runway — all recorded from the actual day. Only your hands on the controls are new.

The equities desk mid-session
1 · Window catalog2 · Chart3 · Order entry4 · Transport
Every number on this screen is real history except your orders and account.

Real

  • Every quote and every print. NBBO updates, bid/ask sizes, trade prints and their condition codes come from tick-level historical data for that ticker on that date.
  • Scanner alerts. Top Leading Gainers and High-of-Day Momentum hits fire at the exact timestamps they fired live, in the same order.
  • News. Headlines appear as the replay clock passes their publish time.
  • Fundamentals. Float and shares outstanding as of the replay date, from SEC filings, with splits applied.
  • The clock. Every timestamp on the desk is the replay clock, never your wall clock.

Simulated

  • Your orders. They never leave the building. No real capital moves.
  • How they fill. A fill engine evaluates each order against the real NBBO with a drawn latency, walk-the-book mechanics for marketable orders, and queue position for resting limits. See Reading a fill.
  • Your account. Cash, buying power, P&L — all tracked, none real.

Deterministic

Same ticker, same date, same start time, same seed → the same tape, the same alerts, and the same latency draws. You can replay a day as many times as you want and compare your decisions, not the dice.