The interval between the sinus node discharges, i.e. the sinus node cycle length or SS interval, determined by dividing the interval between the first P weave of each group (2.32.seconds) by the number of P waves in this envelope (4) is 0.58 seconds, a rate of 104 per minute. The assumed location of the sinus node discharge to the onset of atrial activation (the onset of the P wave) in the first beat of the group is shown in the ladder diagram. This demonstrates the progressive lengthening of the SA interval prior to the block.