  double curtime;
  double ms;
  double minutes;
+ double time_dif;
+ String data;
  
   void setup()
  {

 
 void loop()//Measure RPM
 {
   if (revs >= 2) {
     curtime = millis();
     ms = curtime - timeold;
     minutes = ms/1000/60;

     timeold = millis();
     ipm = rpm*2.0*pi*r; //inches per minute
     car_speed = ((ipm*60)/12)/5280;
     data = String(rpm);
     data.concat(",");
     data.concat(String(car_speed));
     revs = 0;
     Serial.println(data);
   }
  }
  
