int ldr = A0;
int ldr2 = A1;
double speed,time,distance = 100;//100cm = 1m

double CT = 0;
double LT = 0;

void setup() {
  // put your setup code here, to run once:
Serial.begin(9600);
pinMode(ldr,INPUT);
pinMode(ldr2,INPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
if(analogRead(ldr)<500){
  CT = millis()/1000.0;
}
else if(analogRead(ldr2)<500){
  LT  = millis()/1000.0;
  time = LT - CT;
}
else if(analogRead(ldr)>500 && analogRead(ldr2)>500){
  display_speed();
}
}
void display_speed(){
  speed = time/distance;
  Serial.println(" m/s");
  Serial.print(speed);

}