Final answer:
Breath testing tends to underestimate BAC by about 10% due to various factors.
Step-by-step explanation:
Breath testing tends to underestimate Blood Alcohol Concentration (BAC) by about 10%.
The Breathalyzer device measures the ethanol concentration in a person's breath, which is directly proportional to the blood alcohol level.
However, the accuracy of breath testing can be influenced by various factors such as metabolism, lung capacity, and calibration of the device.