This document discusses metrics for digital marketing. It distinguishes between "vanity metrics" that don't provide useful information for improving performance, and "actionable metrics" that can be used to take action and impact key performance indicators (KPIs). The document provides an example of implementing call tracking to measure metrics like number of calls, call length, and source channels. It also discusses how to establish KPIs based on business objectives and channels, and how to react to metric data by validating strategies with clients and testing message and content variations.