<p>“If the number of nodes that agree exceeds <strong>2/3</strong>, the blocks or transactions of clients will be accepted”</p>

<p>Practical Byzantine fault tolerance (pBFT) : <strong>(n - 1) / 3</strong></p>

<p>I read those 2 things in a PDF that a friend of mine sent me.</p>

<p>The question is: are those numbers (2/3) or “(n-1)/3” constant? Or those numbers are established by the developers.</p>

<p>What makes those numbers? What’s the reason for 2/3 and not 2.5/3 ?  Or why not <strong>(n - 2 ) / 3</strong></p>

CC BY-SA 4.0
2019-02-15T19:48:06.317Z
Possible duplicate of [Byzantine fault-tolerant consensus - Why 33% threshold](https://bitcoin.stackexchange.com/questions/58907/byzantine-fault-tolerant-consensus-why-33-threshold)
404 User not found
CC BY-SA 4.0
2019-02-15T20:02:18.707Z
It talks about why those numbers but not how they are measured
Juan
CC BY-SA 4.0
2019-02-15T22:55:00.987Z
Where are you getting those nonsense numbers from? Those don't reflect anything about how the network operates at all.
Claris
CC BY-SA 4.0
2019-02-15T23:20:28.053Z
They are not nonsense. They are written on the Practical Byzantine fault PDF. It does reflect how the network operates (Not for Bitcoin’s blockchain though)
Juan
<blockchain><consensus>
How is the fault tolerance measured?
Juan
# How is the fault tolerance measured?

(Asked by: username_0 on 2019-02-15)

“If the number of nodes that agree exceeds **2/3**, the blocks or transactions of clients will be accepted”

Practical Byzantine fault tolerance (pBFT) : **(n - 1) / 3**

I read those 2 things in a PDF that a friend of mine sent me.

The question is: are those numbers (2/3) or “(n-1)/3” constant? Or those numbers are established by the developers.

What makes those numbers? What’s the reason for 2/3 and not 2.5/3 ? Or why not **(n - 2 ) / 3**

**Tags:** blockchain, consensus

> **Comments:**
> **username_1**: Possible duplicate of [Byzantine fault-tolerant consensus - Why 33% threshold](https://bitcoin.stackexchange.com/questions/58907/byzantine-fault-tolerant-consensus-why-33-threshold)  
> **username_0**: It talks about why those numbers but not how they are measured  
> **username_2**: Where are you getting those nonsense numbers from? Those don't reflect anything about how the network operates at all.  
> **username_0**: They are not nonsense. They are written on the Practical Byzantine fault PDF. It does reflect how the network operates (Not for Bitcoin’s blockchain though)  

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