# Blockchain course 3/16

## PoW property 1/3 diffcult of computing

PoW(proof of work)

* in 2020, about \\( 10^{21} \\) hash/block

## PoW property 2/3

* node re-caculate the target (256 byte) 2016 every block

## PoW property 3/3
* Nonce must be publiced
* H(nonce )

## Mining economic

## Rule of game