What device is used to mark the ECG paper?

The device used to mark the ECG paper is the stylus. A stylus is a pointed instrument that, when heated or electrically charged, can inscribe waveforms directly onto the ECG paper. This method is essential for creating accurate and permanent records of the heart's electrical activity during an electrocardiogram examination. The stylus allows for precision and clarity in the recording of the various waveforms and intervals on the ECG, which are critical for diagnosis and evaluation of cardiac health.

In contrast, a pencil, ink pen, or highlighter are not suitable tools for marking ECG paper intended for diagnostic purposes. While they may mark the paper, the markings would not be electrically generated representations of the heart's activity and may not be permanent or precise enough for medical evaluation. The stylus remains the standard tool specifically designed to produce reliable and interpretable ECG tracings.