The userguide says:
![userguide][1]

But I find another explanation saying that，the -Z should be set to the size of genome times 2.

I am in a mess now. How should I set the -Z , and I also want to know what's the E-value?



  [1]: /media/images/092d9bed-d881-41c3-9105-d1c0639c
To calculate Z please visit this [link](https://docs.rfam.org/en/latest/genome-annotation.html) and use the function 

```
esl-seqstat my_reference.fasta*
```
* reference fasta should be your genome. 

E-score: 
The E-value is the statistical significance of the hit: the number of hits we’d expect to score this highly in a database of this size (measured by the total number of nucleotides) if the database contained only nonhomologous random sequences. The lower the E-value, the more significant the hit.

Z: This option ensures that the reported E-values are accurate.

I hope that his helps: 
