What does the "pri" value stand for?

[realdevnullius]

tmp ready phases dst plots GBfree inbnd phases pri
I understand all the values for these columns, except for the plotman pri value. What does it stand for? Priority? How's it determined and how do I interpret those numbers?

Just wondering :) My current values are: 27, 25, 62, 66, 58

[realdevnullius]

From the readme:
pri = the priority computed for the archive job to move the plots away.