The problem is that it takes an entire second to count RPM, which will delay the updates to your LCD. This may be acceptable or not. If you have a fast RPM and don’t care about precision, you can reduce the sampling interval to 500 msecs or even 250 msecs.
One other way to count RPM is to count the time in msecs it takes between each HIGH of the rpm sensor, then use this formula: rpm = 60 secs/min * 1000 msecs/sec * timebetweenpulses msecs
What some people do is use the pulses-per-one-second method for fast RPMs and then switch to time-between-pulses for slow RPMs.
Karen