What is an ECG commonly used to measure?

An ECG, which stands for electrocardiogram, is a test that records the electrical activity of the heart over a period of time. It is primarily used to assess the heart's rhythm and electrical conduction system, providing valuable information about heart rate and other cardiac conditions. The electrocardiographic signals reflect how well the heart is functioning and can help detect issues such as arrhythmias, ischemic heart disease, and other cardiac abnormalities.

In this context, the answer choice referring to the electrocardiogram itself is accurate as it defines what an ECG is and encompasses its purpose. While the ECG does indirectly help in measuring heart rate, it is primarily recognized by its full terminology, which is essential for understanding its function in a medical setting.

The other choices relate to different physiological measurements: blood pressure is determined through a sphygmomanometer, and oxygen levels are typically measured via pulse oximetry. Therefore, identifying the ECG as an electrocardiogram contextualizes its use in cardiac monitoring and assessment.