# Order Book XPress protocol's order book is fully on-chain and works similarly to centralized exchanges. Orders are matched based on price-time priority. In contrast to some other on-chain order books, there is no upper bound on the number of orders that can be simultaneously placed on XPress. All prices allow up to 6 digits of precision, enabling tick sizes of less than 0.001%. --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.xpressprotocol.com/trading/order-book.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.