Average plus minus

[messyshack]

What does the average plus/minus column on my stat sheet tell me? From what I can tell the numbers aren't a percentage change or the number of pins my average has changed.

[litefrozen]

The plus/minus column shows how much your score was over or under average that night.
Example-
Say you have 200 average(your ave series would be a 600) and that night you shoot a 630 series that would be +30.
Now say you only shot a 580 series that would be -20.