An advertising planimeter is a tool used in marketing and advertising to measure the effectiveness of a campaign or advertisement. It calculates the reach, frequency, and impact of an ad by analyzing data such as audience demographics, engagement rates, and conversion rates. This allows advertisers to make informed decisions about their advertising strategies and optimize their campaigns for maximum impact. The use of an advertising planimeter helps businesses to accurately track the success of their marketing efforts and make data-driven decisions to achieve their advertising goals.