Market Execution Mechanics Tutorial

A step-by-step tutorial explaining how orders are recorded, matched, and executed, and how prices are formed, using a small market to make every rule explicit.

  • 25 lessons
  • ~1 hr 4 min to 1 hr 22 min total reading time
  • Focus: order matching and price formation

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What’s inside

  • Order book basics: bids, asks, and the trade tape
  • Matching rules: price priority first, time priority second
  • Execution patterns: partial fills, multi-price execution, crossed orders
  • How price is recorded: discrete trades, repeated prices, and gaps
  • How to read activity: heavy trading at one price vs fast moves with few trades

What this tutorial challenges

  • The idea that prices move smoothly
  • The belief that more trading means more price movement
  • The assumption that the last price influences the next trade
  • The notion that charts explain execution

Contents

Introduction

Before charts, indicators, or opinions, we define what a market actually records and what a price really is.

  1. How Orders Execute and Prices Are Recorded — A Very Small Apple Market 2.0-3.0 min

Core Mechanics

We establish the basic mechanics of a market: how orders are recorded, why most never trade, and the exact conditions required for a trade to exist at all.

  1. Market Records 0.5-1.0 min
  2. A Single Ask Appears 0.5-1.0 min
  3. A Buyer Appears Below the Ask 2.0-2.5 min
  4. The First Trade Is Executed 4.0-5.0 min
  5. Sell Order Added to the Asks Ledger 1.0-1.5 min
  6. A Trade Occurs at a New Price 1.5-2.0 min
  7. A New Trade Does Not Require a New Price 2.5-3.5 min

Execution Structure

Execution is not a single event. It is a sequence of steps, each producing specific and observable changes in the book and the trade tape.

  1. Partial Execution Creates Multiple Trades 2.0-2.5 min
  2. Execution Priority Is Determined by Time 2.5-3.0 min
  3. Orders Can Be Removed Without Trading 1.5-2.0 min
  4. Execution Price When Orders Cross 4.0-5.0 min

Multi-Price Execution

A single order can execute across multiple prices, producing several trades without the price “moving through” intermediate levels.

  1. One Order Can Execute Across Multiple Prices 4.0-5.0 min
  2. One Order Can Execute Across Multiple Prices (Sell-Side Mirror) 3.5-4.5 min
  3. One Order Can Execute Across Multiple Prices (Sell-Side Confirmation) 2.5-3.0 min

Price–Time Priority

When prices are equal, time—not intention, size, or urgency—determines execution order. These lessons formalize that rule and its consequences.

  1. Common Misconceptions About Order Execution 3.0-4.0 min
  2. When Prices Are Equal, Time Determines Execution 3.0-4.0 min
  3. Time Determines Execution When Bid Prices Are Equal 3.0-4.0 min
  4. FIFO Applies Even When Orders Are Partially Executed 2.5-3.5 min
  5. How Price Changes Interrupt FIFO 3.0-3.5 min

Trade Tape Interpretation

Here we shift perspective: away from the book and toward the trade tape, examining what price records reveal and what they do not.

  1. The Same Price Can Appear Multiple Times Over Time 3.5-4.5 min
  2. Prices Change in Steps, Not Continuously 2.5–3.5 min
  3. Orders Can Arrive Between Executions 2.5–3.5 min

Activity vs Price

These lessons separate price movement from trading activity, showing how large price changes can occur with little trading and vice versa.

  1. Heavy Trading Can Occur at a Single Price 2.0–2.5 min
  2. Rapid Price Changes Can Occur With Little Trading 2.0-2.5 min

Putting It All Together

All rules are assembled into a single, consistent execution model with no hidden assumptions.

  1. Final Lesson — Orders, Executions, and Prices 3.0-4.0 min

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