This document discusses various definitions and concepts related to blood alcohol concentration (BAC) testing. It provides BAC levels for blood, breath, and urine. It notes that the typical blood-breath partition ratio used is 2100:1 but that this ratio can vary significantly between individuals and within individuals over time. It discusses factors like temperature that can affect BAC readings and notes that using a single partition ratio can lead to over or underestimation of BAC levels in some people.