High Precision Scale with Arduino

#include <LiquidCrystal_I2C.h>
#include <HX711.h>

HX711 scale(A1, A0); 
LiquidCrystal_I2C lcd(0x3F,16,2);


// 
volatile float newWeight;
volatile float prevWeight;
volatile float money;
volatile float item;
volatile float change;
volatile float flag;
volatile int show = 1;
volatile float itemWeight;
volatile int amount;

int tara = 4;
unsigned long int lastTime;

int up = 2;
int down = 3;
volatile int pos = 1;


void setup() {
  lcd.init();                                         //   
  lcd.backlight();                                    //  
  scale.set_scale(-1537.34);                          //    (   )
  scale.tare();                                       //  
  prevWeight = 0;                                     //    
  scale.power_up();

  Serial.begin(9600);
  
  pinMode(tara, INPUT);
  pinMode(up, INPUT);
  attachInterrupt(0, dec, RISING);
  pinMode(down, INPUT);
  attachInterrupt(1, inc, RISING);

}

void myClear() {
    lcd.setCursor(0,0);
    lcd.print("                ");
    lcd.setCursor(0,1);
    lcd.print("                ");
    lcd.setCursor(0,0);
  }

void reload() {
  prevWeight = 0;
  newWeight = 0;
  money = 0;
  item = 0;
  change = 0;
  show = 1;
}

void dec() {
  reload();
  if (pos > 1) {
    pos -= 1; 
  }
  else {
    pos = 4;  
  }
}

void inc() {
  reload();
  if (pos < 4) {
    pos += 1;  
  }
  else {
    pos = 1;  
  }    
}

void analysis() {
  if (change > 1.00 && change < 2.40) {               // 1c           
    money += 1;
    flag = 1.25;
  }
  else if (change > 2.80 && change < 3.15) {          // 2c
    money += 2;
    flag = 2.50;
  }
  else if (change > 3.70 && change < 3.99) {          // 5c
    money += 5;
    flag = 3.80;
  }
  else if (change > 4.00 && change < 4.15) {          // 10c
    money += 10;
    flag = 4;
  }
  else if (change > 5.50 && change < 6.80) {          // 20c
    money += 20;
    flag = 6;
  }
  else if (change > 7.60 && change < 7.95) {          // 50c
    money += 50;
    flag = 7.80;
  }
  else if (change > 7.30 && change < 7.50) {          // 1E
    money += 100;
    flag = 7.40;
  }
  else if (change > 8.20 && change < 9.00) {          // 2E
    money += 200;
    flag = 8.50;
  }
}

//  :
void standard() {
  lcd.setCursor(0,0);
  lcd.print(" Standard mode! "); 
  lcd.setCursor(0,1);                                 //    1  2 !
  lcd.print("Weight: ");
  if (prevWeight != round(scale.get_units(10)) ) {     //   ,
    newWeight = scale.get_units(10);                   //     
  }
  lcd.setCursor(9,1);
  if (newWeight < 0) { scale.tare(); }
  else { lcd.print(newWeight); }
  prevWeight = newWeight;                             //    

}
///////////////////////////////////

void multiMoney() {
  lcd.setCursor(0,0);
  lcd.print("  Money multi!  ");
  lcd.setCursor(0,1);
  lcd.print("Euro: ");
  if (prevWeight != round(scale.get_units(10)) ) {    
    newWeight = scale.get_units(10);
    change = newWeight - prevWeight;
    analysis();
    lcd.setCursor(6,1);
    lcd.print(money / 100.00);
    prevWeight = newWeight;          
  }
}
//////////////////////////////////////////

void massMoney() {
  if (prevWeight != round(scale.get_units(20)) ) {    
    newWeight = scale.get_units(20); 
    change = newWeight - prevWeight;
    prevWeight = newWeight;
    if (change > 1) {
      lcd.setCursor(0,1);
      lcd.print("C:");
      lcd.setCursor(2,1);
      lcd.print(show);
      lcd.setCursor(7,1);
      lcd.print("A:");
      lcd.setCursor(10,1);
      lcd.print(show * money / 100);
      show = show + round(change / flag);  
    }
  }
}
//////////////////////////////////////

void itemsMass() {
  if (prevWeight != round(scale.get_units(10)) ) {    
    newWeight = scale.get_units(10);
    change = newWeight - prevWeight;
    amount = round(change / itemWeight);
    lcd.setCursor(0,1);
    lcd.print("Items: ");
    lcd.print(amount);
    lcd.setCursor(9,1);
    lcd.print("W:");
    lcd.print(newWeight);
  }
}
//////////////////////////////////////////


void loop() {
  if (millis() - lastTime > 100) {
    if (digitalRead(tara) == 1) {
      reload();
      scale.tare();
    }
    lastTime = millis();
  }
  
  if (pos == 1) {
    myClear();
    lcd.setCursor(4,0); 
    lcd.print("Standard");
    delay(1000);
    myClear();
    while (pos == 1) {
      standard();
    } 
  }

  else if (pos == 2) {
    myClear();
    lcd.setCursor(3,0);
    lcd.print("Money multi");
    delay(1000);
    myClear();
    while (pos == 2) {
      multiMoney();  
    }
  }

  else if (pos == 3) {
    myClear();
    lcd.setCursor(3,0);
    lcd.print("Money mass");
    delay(1000);
    myClear();
    lcd.print("Place ONE coin!"); 
    while (money == 0) {
      if (prevWeight != round(scale.get_units(10)) ) {    
        newWeight = scale.get_units(10);
        change = newWeight - prevWeight;
        analysis();
        lcd.setCursor(0,1);
        lcd.print(money / 100);
        prevWeight = newWeight;          
      }
    }
    myClear();
    lcd.print("Counting ");
    if (money < 100) {
      lcd.setCursor(10,0);
      lcd.print(money);
      lcd.print("c");
    }
    else {
      lcd.setCursor(10,0);
      if (money == 100) { lcd.print("1 Euro"); }
      else { lcd.print("2 Euro"); }
    }
    prevWeight = 0;
    newWeight = 0;
    change = 0;
    while (pos == 3) {
      massMoney();
    }
  }
  

  else if (pos == 4) {
    myClear();
    lcd.setCursor(3,0);
    lcd.print("Items mass");
    delay(1000);
    myClear();
    myClear();
    lcd.print("Place ONE item!");
    while (newWeight < 1) {
      if (prevWeight != round(scale.get_units(10)) ) {    
        newWeight = scale.get_units(10);
        itemWeight = newWeight - prevWeight;
      }
    }
    itemWeight = newWeight - prevWeight;
    lcd.setCursor(0,0);
    lcd.print("Item weight:");
    lcd.print(itemWeight);
    while (pos == 4) {
      itemsMass();
    }
  }
}