Measuring HC-SR04 always change

Using Arduino Sensors
5

I'm using this sensor to measure the human height.
And this is the code i used.
//--------------------------------------------
#define ECHOPIN 3
#define TRIGPIN 2
#include <LiquidCrystal.h>
LiquidCrystal lcd(13, 12, 11, 10, 9, 8 ) ;
int H2,HT,H1;

void setup(){
lcd.begin(16, 2);
lcd.print(“Height”);
lcd.setCursor(0, 1);
lcd.print(“TB=”);
pinMode(ECHOPIN, INPUT);
pinMode(TRIGPIN, OUTPUT);
delay(1000);
HT=200;
}

void loop(){
digitalWrite(TRIGPIN, LOW);
delayMicroseconds(2);
digitalWrite(TRIGPIN, HIGH);
delayMicroseconds(10);
digitalWrite(TRIGPIN, LOW);
int distance = pulseIn(ECHOPIN, HIGH);
distance= distance/58;
H2=HT-distance;
lcd.setCursor(3, 1);
lcd.print(H2);
lcd.print(” cm “);
delay(1000);
}
//--------------------------------------------

I put the sensor at 2 meters of height, so i get HT = 200. And the Object is a stainless plate. I have to move the plate above the head to get the best rebound area.

is there something false on my code?
Thank you very much before.