You are managing a high-traffic web application that uses a microservice architecture. The application's home page features various widgets displaying content like current weather, stock prices, and news headlines. Each widget's content is sourced from a dedicated microservice. The main serving thread, which organizes the homepage layout, sometimes encounters microservice failures, resulting in the homepage being displayed with incomplete content. While users prefer having partial content to none, frequent occurrences of this degraded mode are unsatisfactory. To maintain an acceptable level of user experience, you aim to establish a Service Level Objective (SLO). What Service Level Indicator (SLI) should you choose to effectively measure this aspect?