#include <HCSR04.h>

HCSR04 Hcsr04(7, 6); //initialization class HCSR04 (trig pin , echo pin)

//Variables declaration

//Values to input manually
float container_H = 21.0;   //Container Height (cm)
float base_surface = 324.0; //Container base surface (Square cm)


//Calculated values
float liquid_H;             //liquid heigth (cm)
float distance;             //liquid distance from sensor (cm)
float volume;               //final result: volume (cubic< cm)



void setup()                //this part of program runs only at the start
{
  Serial.begin(9600);       //Serial port initialization
}



void loop()                 //this part of program is cyclic
{
  distance = (Hcsr04.dist());             //distance reading from sensor
  liquid_H = (container_H - distance);    //liquid level calculation
  volume = (base_surface * liquid_H);     //volume calculation

Serial.print ("Volume ");                  //print volume
Serial.print (volume);                  //print volume  
  Serial.println (" cm3");
  Serial.print ("Height ");                //print liquid height
  Serial.print (liquid_H);                //print liquid height
  Serial.println (" cm");
  Serial.println();
  delay(1000);                           //delay to the next cycle
}