int pin = 13;
unsigned long RPM;
unsigned long duration;

float W;
void setup()
{
Serial.begin(9600);
pinMode(pin, INPUT);
}
void loop()
{
duration = pulseIn(pin, HIGH);
if(duration > 5000)
{
RPM = (1000000*60/duration);
Serial.print(RPM);
Serial.print(" RPM    ");





delay(10); // delay
}
}