achow101 thanks a lot, it all makes sense now. Great explanation. And what you said led me more digging into details.

this is what I understand, in summary;

example for block 540494



so calculated hash must be less than or equal to the target value...



so it is clear to see that the hash is less than the target...

I understand why there are zeros. it is just the representation. it all makes sense now..

Just one more thing, so the nonce has nothing to do with the difficulty number right?  so nonce can be greater than difficulty value? they are not related at all? if they are not related what is the maximum number a nonce can be? when the miner decides to change something in the block?

EDIT: I believe it can be 2147483647 at most. which is the largest 32bit value. so when it hits this number, miner decides to change something else within the block