int inputPin = 2;

unsigned long time1;
unsigned long time2;
int half_revs = 0;

float time = 0;
float rps = 0;

int inBit;

void setup() {
  
  // Open Serial Port
  Serial.begin(9600);
  while (!Serial) {
    // wait for serial port to connect. Needed for Leonardo only
  }
  
  // Config Pins
  pinMode(inputPin,INPUT);
  attachInterrupt(0, tach, CHANGE);
}

void loop() {
  
  half_revs = 0;
  time1 = micros();
  interrupts();
  delay(750);
  noInterrupts();
  time2 = micros();
  
  time = ((float)time2+(float)time1)/2/1e6;
  rps = (half_revs/2)/((time2-time1)/1e6);
  
  if (Serial.available()>0){
    inBit = Serial.read();
    
    Serial.println(time);
    Serial.println(rps);
  }
  
}

void tach()
 {
   half_revs++;
 }