Which wave of human heart out of PQRST is used for determining the heart beat of an individual?
a)	P	b)	QRS	c)	T	d)	RS

(b)

By counting the numbers of QRS complexes that occur in a given time period, one can determine the heart beat rate of an individual. Since the ECGs is obtained from different individuals have roughly the same shape for a given lead configuration, any deviation from this shape indicates a possible abnormality or disease. Hence it is of great clinical significance