The display of 0 for bids and offers in the market depth occurs in two key scenarios: during the pre-open session and in the Periodic Call Auction mechanism. Here’s why this happens:

1. During the Pre-Open Session (9:00 AM to 9:15 AM):

• All market orders (both regular and AMO) placed during the pre-open session are initially assigned a price of 0.
• These orders are termed ‘At the Open’ (ATO) orders.
• The price of 0 is temporary and serves as a placeholder until the equilibrium price is determined during the order matching process.

Key Timeline:

• 9:00 AM - 9:07 AM: Participants place, modify, or cancel orders.
• 9:07 AM - 9:08 AM: Random closure period occurs, during which order matching happens, and the equilibrium price is determined.
• Post 9:08 AM: Market depth is updated to reflect the actual prices of matched orders.

2. During Periodic Call Auction Sessions:

• Similar to the pre-open session, market orders in stocks under the Periodic Call Auction category are also initially priced at 0.
• These stocks are traded in defined auction sessions throughout the day to control volatility and ensure fair price discovery.
• The 0 bids and offers in the market depth indicate that market orders are awaiting price discovery, which happens during the order matching period of each session.

Why Does This Happen?

• Placeholder for Price Discovery: The display of 0 indicates that the orders are market orders and do not have a fixed price yet.
• Transparent Matching Process: This ensures that all participants have equal visibility and a fair opportunity to place their orders before the final price is determined.

When Does the Market Depth Get Updated?

• In the pre-open session, market depth is updated after 9:08 AM, when the equilibrium price is calculated.
• In Periodic Call Auctions, market depth updates occur after the 8-minute order matching period of each auction session.

By displaying 0, the system ensures transparency in the price discovery process while maintaining a structured and fair-trading environment.