Confusion Over Evidence Act Section 29

Kya yeh section 29 ke baar mein confused rehta hoon. Toh ye kya hai, sirf yeh kehne ka adhikar hota hai ki kisi cheez ka presence ya absence hai, to uska koi shasan hai? Ab ek scenario lagata hoon, ek witness kehte hain ki vah ek scene dekha hai, lekin uss scene mein kuch vishay absent the. Lekin ab ye kya hota hai, kya vah witness ka statement evidence ban sakta hai? Maine yeh toh read kiya hai Section 29 mein jo evidence ke baare mein likha hai, lekin to maine abhi clear nahi ki yeh statement evidence kaise ban sakta hai.