Digital Angle Divider

/*=============================================
    Program : Digital Angle Divider
    Author  : wickPro-PC\wickPro
    Time    : 9:30 PM
    Date    : 02/08/2018
    Coded by: Pramod C Wickramasinghe
    E-mail  : wick.pro@gmail.com
    Mobile  : +94774585875
  =============================================*/

#include <Wire.h>
#include "SSD1306Ascii.h"
#include "SSD1306AsciiWire.h"

#define I2C_ADDRESS 0x3C
#define zero 2
#define units 3

SSD1306AsciiWire oled;

int measureValue, unitsVal, zeroVal = 0;
int noOfReadings = 10;
double _value, buff_1, buff_2, buff_3, buff_4, setZero = 0;
//-----------------------------------------------------------------------------

void reading() {

  if (unitsVal % 2 == 0) {
    //_value = (map(measureValue, 0, 1023, 0, 254) / 10.0) ;

    // _value = (-0.0001)*(measureValue)*(measureValue) + (0.3249)*(measureValue) + (40.78) - 1; // 1.0 offset occured

    buff_1 = (-0.00010954) * (measureValue) ;
    buff_2 = buff_1 * (measureValue);
    buff_3 = (0.32620281) * (measureValue);
    buff_4 = buff_3 + 44.64231864;
    _value = buff_2 + buff_4 - setZero;

  } else {
    //_value = (map(measureValue, 0, 1023, 0, 10) / 10.0) ;

    buff_1 = (-0.00000426) * (measureValue) ;
    buff_2 = buff_1 * (measureValue);
    buff_3 = (0.01289839) * (measureValue);
    buff_4 = buff_3 + 1.72506535;
    _value = buff_2 + buff_4 - setZero; // coEff =
  }

  oled.setFont(Callibri15);
  oled.setLetterSpacing(2);
  oled.set2X();
  oled.setCursor(0, 2);
  oled.print("            ");

  if (_value < 1000 && 100 <= _value) {
    oled.setCursor(15, 2);
  } else if (_value < 100 && 10 <= _value) {
    oled.setCursor(28, 2);
  } else if (_value < 10 && 0 <= _value) {
    oled.setCursor(40, 2);
  } else if (_value < 0 && -10 <= _value) {
    oled.setCursor(30, 2);
  } else if (_value < -10 && -100 <= _value) {
    oled.setCursor(20, 2);
  } else if (_value < -100 && -1000 <= _value) {
    oled.setCursor(7, 2);
  } else {
    oled.setCursor(0, 2);
  }

  oled.print(_value);
}
//------------------------------------------------------------------------------
void setup() {

  Wire.begin();
  oled.begin(&Adafruit128x64, I2C_ADDRESS);

  oled.setFont(Callibri11_bold);
  oled.setCursor(0, 0);
  oled.println("Measurement:");
  //oled.setCursor(100, 2);
  //oled.print("mm");
  oled.setCursor(5, 6);
  oled.print("Zero");
  oled.setCursor(100, 6);
  oled.print("Units");

  pinMode(zero, INPUT);
  pinMode(units, INPUT);
}
//------------------------------------------------------------------------------
void loop() {

  if (digitalRead(units) == LOW) {
    unitsVal++;
    delay(100);
  }
  if (digitalRead(zero) == LOW) {
    setZero = 0;
    reading();
    setZero = _value;
    delay(100);
  }
  if (unitsVal % 2 == 0) {
    oled.setFont(Callibri11_bold);
    oled.setLetterSpacing(1);
    oled.set1X();
    oled.setCursor(100, 2);
    oled.print("mm");
  } else {
    oled.setFont(Callibri11_bold);
    oled.setLetterSpacing(1);
    oled.set1X();
    oled.setCursor(100, 2);
    oled.print("inch");
  }

  for (byte i = 0; i < noOfReadings; i++) {
    measureValue = measureValue + analogRead(A0);
    delayMicroseconds(1000);
  }
  measureValue = measureValue / noOfReadings;
  reading();
}