Accurate Speed measurement using the UltraSonic sensor

1const int trigPin = 5;
2const int echoPin = 6;
3
4
5long duration;
6int  FirstDistance=0;
7int SecondDistance=0;
8double speed=0;
9int distance=1;
10float  Time = 2.0;
11float delayedtime = 1000*Time;
12
13void setup()
14{
15pinMode(trigPin,  OUTPUT); 
16pinMode(echoPin, INPUT); 
17Serial.begin(9600); 
18}
19
20
21void  loop()
22{
23GetSpeed();
24
25}
26
27float GetDistance()
28{
29// Clears  the trigPin
30digitalWrite(trigPin, LOW);
31delayMicroseconds(2);
32
33// Sets  the trigPin on HIGH state for 10 micro seconds
34digitalWrite(trigPin, HIGH);
35delayMicroseconds(10);
36digitalWrite(trigPin,  LOW);
37
38// Reads the echoPin, returns the sound wave travel time in microseconds
39duration  = pulseIn(echoPin, HIGH);
40
41//calculating distance
42distance= duration*0.034/2;
43
44//  Prints the distance on the Serial Monitor
45Serial.print("Distance in cm : ");
46Serial.println(distance);
47
48return  distance;
49
50}
51void GetSpeed(){
52 
53   FirstDistance = GetDistance();  //get the first distance
54   
55   delay(delayedtime); //waits 2 seconds depending  on the time declared above ,, feel free to change the value dependng on the resolution  of your sensor 
56   
57   SecondDistance = GetDistance(); //gets the second distance
58   
59   speed = (FirstDistance - SecondDistance)/Time;  // now calculating the  difference 
60   
61 
62//printing the speed on the serial monitor
63  Serial.print("the  speed (cm/s) is  :  ");
64  Serial.println(speed);
65 
66}