How is the "fill%" calculated in the alignment result file of the MSDIAL software?

How is the "fill%" calculated in the alignment result file of the MSDIAL software? 
The picture is from my result file.
 I can't match the value of "fill%" in my result file.



<img width="1240" height="779" alt="Image" src="https://github.com/user-attachments/assets/1f9a0e97-1462-4b0d-bb1d-583757f9b990" />