What must be calibrated regularly to ensure the accuracy of the Intoxilyzer 9000?

Regular calibration of the calibration control is essential for the Intoxilyzer 9000 to ensure that the device provides accurate and reliable readings. The calibration control consists of standard solutions with known alcohol concentrations, which help verify that the machine is responding correctly to breath samples.

When the Intoxilyzer is regularly calibrated using these controls, any drift in the measurements can be identified and corrected, ensuring that the results of breath analyses reflect the true levels of alcohol in a person's system. This process is crucial because environmental factors, wear and tear over time, and the inherent sensitivity of the device can all impact its performance.

Other options, such as the breath sample, the operator, or the subject, do not directly influence the calibration of the device itself. While the breath sample is what is being measured and the competency of the operator can affect procedural integrity, it is the calibration control that specifically ensures the accuracy of the machine's readings. Regular calibration thus upholds the integrity of the breath alcohol testing process.