# PNL Understanding the difference between mark price and last price is crucial for NFT trading on Ariable perpetual swaps. The last price is the most recently traded price of a perpetual contract, and it reflects the real-time traded price. While the last price is based on the supply and demand of the perpetual contract, it may deviate from the actual price of its underlying asset. To ensure more stable and reliable pricing, Ariable uses the mark price, which is an estimated fair value of the perpetual contract that considers the reasonable worth of its underlying asset. The mark price helps prevent unwarranted liquidation resulting from market manipulation or illiquidity. The mark price is used for unrealized PnL calculations and liquidation, ensuring that liquidations are not unjustified due to temporary fluctuations in the last price. However, the last price is still the essential market price that every user trades on, while the mark price is an indicator that monitors a position's risk and is not used in actual trading. --- # 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://ariable.gitbook.io/untitled/product/nft-trading/pnl.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.