Use an ECG simulator set to 60 bpm. At a chart speed of 25 mm/sec and a pulse interval of 1,000 msec (60 bpm on an ECG simulator), the distance between the first and last of five successive QRS complexes should be 100 ±2 mm; at a chart speed of 50 mm/sec, the distance between the first and last of five successive peaks QRS complexes should be 200 ±4 mm.