Scale object so it always stand on its parent plane

scale.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class scale : MonoBehaviour
{
    // Scale represented as single variable
    [Range(0.0f, 5.0f)]
    public float objectScale = 1.0f;

    // Scale and position represented as xyz vectors
    private Vector3 scaleChange, positionChange;
    // Original Y position of the object
    private float originalY = 0.0f;
    // Y position calculated during Update cycle
    private float newY = 0.0f;

    // Start function that is called once so it kepps all ORIGINAL values
    void Start()
    {
        // Here we save our original y position and never change it further
        originalY = transform.localPosition.y;
    }

    // Update is called once per frame
    // I use localPosition, it means that I move my object relative to parent plane
    // if object is not child of any parent, then our target plane is XZ plane
    void Update()
    {
        /*
         * This is where all magic happens.
         * So we need to keep our object stnading on the parent plane(globally XZ plane)
         * First of all we need to understand how our original y relates to our original scale:
         * well, it is simply originalY/1.
         * Consequently, we get ourself a proportion 
         * !!! Y/objectScale = originalY/1 !!!
         * From that we need to get Y, it equals (objectScale * originalY) / 1 (we can drop division by one)
         */
        newY = objectScale * originalY;
        positionChange = new Vector3(transform.localPosition.x, newY, transform.localPosition.z);
        
        // Set our new position
        transform.localPosition = positionChange;

        // Change scale
        scaleChange = new Vector3(objectScale, objectScale, objectScale);
        transform.localScale = scaleChange;
    }
}