Speedometer ReedSwitch

#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C lcd(0x27, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE);

const int reedPin = 2;

float radius = 18;
float circumference;

int reedState;
int lastReedState = LOW;

long timer = 0;
float kmh = 0.00;
float maximal = 0.00;

// the following variables are unsigned longs because the time, measured in
// milliseconds, will quickly become a bigger number than can be stored in an int.
unsigned long lastDebounceTime = 0;
unsigned long lastDebounceTime1 = 0;
unsigned long lastDebounceTime2 = 0;
unsigned long debounceDelay = 20;    // the debounce time; increase if the output flickers

unsigned long previousMillis13 = 0;
unsigned long previousMillis1 = 0;

void setup()
{
  circumference = 2*3.14*radius; // 89.92
  pinMode(reedPin, INPUT);

  Serial.write(12);//clear

  lcd.begin(16, 2);
  Serial.begin(9600);
}

void loop() {
  // read the state of the switch into a local variable:
  int reading = digitalRead(reedPin);

  // check to see if you just pressed the button
  // (i.e. the input went from LOW to HIGH), and you've waited long enough
  // since the last press to ignore any noise:

  // If the switch changed, due to noise or pressing:
  if (reading != lastReedState) {
    // reset the debouncing timer
    lastDebounceTime = millis();
  }

  if ((millis() - lastDebounceTime) > debounceDelay) {

      if (reading != reedState) {
        reedState = reading;

        if (reedState == HIGH) {
          lastDebounceTime1 = millis();
          timer = lastDebounceTime1 - lastDebounceTime2;
        }else{
          lastDebounceTime2 = millis();
        }

        Serial.println(timer);

        kmh = (56.8*float(circumference))/float(timer);//calculate miles per hour
      }
  }

  // set the LED:
  //digitalWrite(ledPin, ledState);

  // save the reading. Next time through the loop, it'll be the lastButtonState:
  lastReedState = reading;

  if(millis() - previousMillis13 >= 500){
    previousMillis13 = millis();
    displayKMH();
    if(kmh > maximal){
      maximal = kmh;
    }
    displayMAX();
  }
  if(millis() - lastDebounceTime2 >= 2000){
    kmh = 0.00;
  }
}

void displayKMH(){
  lcd.setCursor(0, 0);
  lcd.print("      ");
  lcd.setCursor(0, 0);
  lcd.print(kmh);
  lcd.setCursor(6, 0);
  lcd.print(" KM/H  ");
}

void displayMAX(){
  lcd.setCursor(0, 1);
  lcd.print(" MAX ");
  lcd.print(maximal);
  lcd.setCursor(11, 1);
  lcd.print(" KM/H  ");
}