What part of an ECG machine moves against the tracing paper to record the waves of the ECG cycle?

The part of an ECG machine that moves against the tracing paper to record the waves of the ECG cycle is called the stylus. The stylus heats up and creates an ink mark on the moving paper as it records the electrical activity of the heart, producing the characteristic waveform of the ECG. The paper moves at a constant speed, allowing for a continuous representation of the heart's electrical activity over time.