These .2da's have 60 rows (numbered 0 to 59), even though only 20 rows are relevant (since base attack advancement stops depending on class after character level 20).
|ID (no actual name)||Row numbers for the benefit of human readers. The game engine ignores the value in this field, instead generating sequential row numbers as the file is read. It is good practice to keep the entries in this field sequentially numbered to avoid confusion.|
The class level to which this row applies is the row number plus one.
|BAB||The base attack achieved at this class level (row number plus one).|
There are three files of this type provided in the standard game, one for each of the standard base attack progressions. Specifically, the standard files of this type are
cls_atk_2.2da(+3/4 levels), and