When first pulse comes, we start counter by using timer counter function in arduino that is millis();. And take first pulse counter value form millis();. Then we wait for five pulses. After getting five pulses we again take counter value in time2 and then we substarct time1 from time2 to take original time taken by five pulses. And then divide this time by 5 times for getting single pulse time. Now we have time for single pulse and we can easily find the pulse in one minute, deviding 600000 ms by single pulse time.