Analog Speedometer Using Arduino and IR Sensor

#include<LiquidCrystal.h>
LiquidCrystal lcd(A5,A4,A3,A2,A1,A0);
#include <Stepper.h>
const int stepsPerRevolution = 200;  // change this to fit the number of steps per revolution
Stepper myStepper(stepsPerRevolution, 8, 9, 10, 11);
volatile byte REV; 
unsigned long int rpm,RPM;
unsigned long st=0; 
unsigned long time; 
int ledPin = 13;  
int led = 0,RPMlen , prevRPM; 
int flag = 0;     

int flag1=1;
#define bladesInFan 2
float radius=4.7;   // inch
int preSteps=0;
float stepAngle= 360.0/(float)stepsPerRevolution;
float minSpeed=0;
float maxSpeed=280.0; 
float minSteps=0;
float maxSteps=maxSpeed/stepAngle;

void setup() 
{
  myStepper.setSpeed(60);
  Serial.begin(9600);
  pinMode(ledPin, OUTPUT);
  lcd.begin(16,2);
  lcd.print("Speedometer");
  delay(2000);
  attachInterrupt(0, RPMCount, RISING); 
}

void loop() 
{
    readRPM();
    radius=((radius * 2.54)/100.0);  // convering in meter
    int Speed= ((float)RPM * 60.0 * (2.0 * 3.14 * radius)/1000.0);
    // RPM in 60 minute, diameter of tyre (2pi r) r is radius, 1000 to convert in km
    int Steps=map(Speed, minSpeed,maxSpeed,minSteps,maxSteps);
   
   if(flag1)
   {
    Serial.print(Speed);
    Serial.println("Kmh");
     lcd.setCursor(0,0);
     lcd.print("RPM: ");
     lcd.print(RPM);
     lcd.print("           ");
     lcd.setCursor(0,1);
     lcd.print("Speed: ");
     lcd.print(Speed);
     lcd.print(" Km/h       ");
    flag1=0;
   }
    int currSteps=Steps;
    int steps= currSteps-preSteps;
    preSteps=currSteps;
    myStepper.step(steps);
}

int readRPM()
{ 
  if(REV >= 10 or millis()>=st+1000)                  //  IT WILL UPDATE AFETR EVERY 10 READINGS or 1 second in idle
  {           
     if(flag==0)                 
       flag=1;                      
     rpm = (60/2)*(1000/(millis() - time))*REV/bladesInFan;  
     time = millis();                            
     REV = 0;
     int x= rpm;                 
     while(x!=0)
     {
       x = x/10;
       RPMlen++;
     }       
     Serial.println(rpm,DEC);
     RPM=rpm;
     delay(500);
     st=millis();
     flag1=1;
   }
}

void RPMCount()                        
 {
   REV++;                              
   if (led == LOW)
   {
     led = HIGH;                         
   } 
   else
   {
     led = LOW;
   }
   digitalWrite(ledPin, led);
 }