This guide outlines a manual technical workflow for identifying the specific code change responsible for a regression within the massive Chromium repository. By leveraging the git bisect command alongside Chromium’s specialized depot_tools, developers can systematically navigate through version history to isolate bugs. A critical requirement of this process is using gclient sync at every step to ensure that external dependencies remain consistent with the main project's state. The text explains how to translate version numbers into Git revisions and addresses how to manage complex scenarios, such as regressions that cross different release branches. Following these structured steps allows for a reliable investigation even when the testing process requires human intervention rather than full automation.