Methodological differences in the placement of precordial ECG electrodes are a major problem in multicenter clinical trials and epidemiological studies. Trend analysis and realization of the full potential of computer programs for serial comparison demands reduction of technical sources of variation in the electrocardiogram (ECG) and vectorcardiogram (VCG) and particularly errors in locating ECG electrodes. The ECG electrodes locator described here reduces a major precordial uncertainty in the identification of the midclavicular and the anterior axillary lines. It simplifies positioning and provides a numeric record of the key precordial electrode positions, facilitating control of electrode placement errors in serial recordings.