Dice Value

Hello there,

I have code for calculating dice value... they using dot product to get the value, i want to know about the code. if anyone know about dot product pls explain me or anyone know how to calculate the dice value tell me the logic. Here is the code.

 using UnityEngine;
 using System.Collections;
 
 public class DiceValue : MonoBehaviour 
 {
     public int side=0;
     int CalcSideUp() 
     {
         float dotFwd = Vector3.Dot(transform.forward, Vector3.up);
         if (dotFwd > 0.99f) return 7;
         if (dotFwd < -0.99f) return 4;
         
         float dotRight = Vector3.Dot(transform.right, Vector3.up);
         if (dotRight > 0.99f) return 8;
         if (dotRight < -0.99f) return 3;
         
         float dotUp = Vector3.Dot(transform.up, Vector3.up);
         if (dotUp > 0.99f) return 5;
         if (dotUp < -0.99f) return 2;
         
         return 0;
     }
     
     void Update() 
     {
         int side = CalcSideUp();
         if (side > 0)
         {
             Debug.Log("Side = " + side);
         }
     }
 }

-Prasanna.