The number is accumulative, meaning if you set it to e.g. 30 days vacation allowance in first year, for the next year you have to add another 30 to total 60.
From v7.0 you can also set offset numbers on custom personnel types:
With a click on the total column, that you can enable to show in the Personnel Tree (Toolbox > Settings > Personnel Tree) it will show the numbers for that type.
The User Report attached here shows the numbers as below: