# FAQ: Build your own Mini-Blockchain! - Adding Blocks to the Chain Securely

This community-built FAQ covers the “Adding Blocks to the Chain Securely” exercise from the lesson “Build your own Mini-Blockchain!”.

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This exercise can be found in the following Codecademy content:

## FAQs on the exercise Adding Blocks to the Chain Securely

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previous_hash = (self.chain[len(self.chain)-1]).hash
new_block = Block(transactions, previous_hash)
new_block.generate_hash()
proof = self.proof_of_work(new_block)
self.chain.append(new_block)
return proof, new_block

we use this proof_of_work function to add zeros as per the difficulty level but we do not see any use of it when we output the whole program , i do know why we want pow and also understood this function

def proof_of_work(self,block, difficulty=2):
proof = block.generate_hash()
while proof[:difficulty] != ‘0’*difficulty:
block.nonce += 1
proof = block.generate_hash()
block.nonce = 0
return proof

but still i dont see its significant in our final output however the add_block returns proof and new_node still we get to see only new_node its hash value and previous hash value in the final output. So why did we created such pow for this exercise