This document discusses return on investment (ROI) measurement and calculation for marketers. It explains that ROI is calculated as profit divided by investment. It also discusses factors that influence ROI methodology, such as business size, product uniqueness, and purchasing complexity. The document outlines four types of sales processes and their measurement challenges from last click sales to multi-channel customer journeys. It provides tips on metrics, testing, and tools to measure ROI and concludes that the total ROI is the sum of partial ROIs when measured smartly.