<p>Generally speaking, the difficulty is increased if the “mean time between two succesful mined block” diminishes. It is a so called “closed loop” control system. As a result, the time between two blocks tends to remain stable. The solution having a certain number of zeros is not guaranteed existing, but any solution lower than it is ok for the system, and is accepted, so definitely it exists a set “lower than” where a suitable solution can be found.</p>

CC BY-SA 4.0
2022-05-29T13:14:00.200Z
This answer seems to imply that the difficulty adjusts after every block, however the difficulty only adjusts only every 2016 blocks.
Murch
CC BY-SA 4.0
2022-05-29T20:32:15.587Z
You are right, but how many blocks between two adjustments depends on the algorithm and there exists many possible choices. Specifically  speaking, the control target variable is the “mean time between two blocks”, the number of samples taken to calculate it is, obviously, “more than one”, from 2 to whatever. If 2016 has been chosen for Bitcoin, it’s ok. Adjusted the answer, thank you.
Rick Park
CC BY-SA 4.0
2022-05-29T12:29:32.577Z
2022-05-29T20:33:34.083Z
2022-05-29T20:33:34.083Z
Rick Park
<p>I heard that the complexity of proof of work in blockchain can vary. On what factors does it depend? Is it possible that that proof of work i.e. the required hash starting with certain number of zeros can't be found? What happens then? Do the transaction wait in the queue until the hash is found</p>

<blockchain>
How does blockchain decide the complexity of proof-of-work
Manu Chadha
# How does blockchain decide the complexity of proof-of-work

(Asked by: username_0 on 2022-05-28)

I heard that the complexity of proof of work in blockchain can vary. On what factors does it depend? Is it possible that that proof of work i.e. the required hash starting with certain number of zeros can't be found? What happens then? Do the transaction wait in the queue until the hash is found

**Tags:** blockchain


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## 1 answers

### Answer by username_1 on 2022-05-29. Score: 0

Generally speaking, the difficulty is increased if the “mean time between two succesful mined block” diminishes. It is a so called “closed loop” control system. As a result, the time between two blocks tends to remain stable. The solution having a certain number of zeros is not guaranteed existing, but any solution lower than it is ok for the system, and is accepted, so definitely it exists a set “lower than” where a suitable solution can be found.

> **Comments:**
> **username_2**: This answer seems to imply that the difficulty adjusts after every block, however the difficulty only adjusts only every 2016 blocks.  
> **username_1**: You are right, but how many blocks between two adjustments depends on the algorithm and there exists many possible choices. Specifically  speaking, the control target variable is the “mean time between two blocks”, the number of samples taken to calculate it is, obviously, “more than one”, from 2 to whatever. If 2016 has been chosen for Bitcoin, it’s ok. Adjusted the answer, thank you.  

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