Thank you both for your responses, this clears up a lot of confusion.

--- In firebird-support@yahoogroups.com, "darklord28099" <zulloje@...> wrote:
>
> Hello all,
>
> I have a question about the growth of files while using nbackup.
> The .nbks created by nbackup seem to grow strangely over the course of usage. For example, on an empty database of 12.4 mb, first nbackups are as follows:
> Level 0 - 12.4 mb.
> Level 1 - 72.1 kb.
> Level 2 - 72.1 kb.
>
> The next runs of level 1 and level 2 backups are usually 80.1 kb in size, but the maximum values reached for the first day are 176.1 kb for a level 1 and 104.1 kb for a level 2.
>
> The next day, a new level 0 backup is made. This new backup is 12.9 mb in size. The maximum size for a level 1 for this day is 352.2 kb and for a level 0 is 120.1 kb. The third day of runs has the database growing to 13.4 mb with a maximum level 1 of 248.2 kb and level 2 of 136.1 kb.
>
> These file size changes occur when there are no transactions performed on the database; the system is simply idling. Is this to be expected with nbackup? Again, there are no changes being performed on the database, so the fluctuations in file sizes is unexpected.
>