What the snapshot shows
An order book distinguishes the demand and supply sides and shows how available quantity is distributed across levels. Its contents depend on the trading mechanism, display completeness and data latency. It is not all information about participants and not a guaranteed volume for a future transaction. Investor.gov warns that the last price may not match actual execution.[4](#source-cm-orders)
Reading price and quantity
To read it, establish whether quantity is expressed in securities, lots or contracts, which sides are shown and what time the snapshot represents. The midpoint between best prices may be a calculation with no opposing order. A narrow spread does not guarantee depth, and high historical turnover does not create a current offer. The SEC treats bid–ask spread separately from other fund expenses.[5](#source-cm-etf) The educational [execution-by-levels table](/guides/liquidity-depth-price-impact/) shows the limits of a static model without investment advice.