The document describes Google's Bid Simulator tool which estimates how an advertiser's keyword performance may change if they adjust their bids. It provides transparency into Google's auction process to help advertisers bid more effectively. The Bid Simulator estimates clicks, costs, impressions and position data based on how the keywords actually performed in the last seven days. This helps advertisers understand the potential impact of different bids without having to experiment directly. The document provides details on how to access and interpret the Bid Simulator's simulations and calculations.