Differential backups, dont make full after "x" backups

[Lmgest]

I can't understand if I use differential backups, why Cobian only did the 1st Full and then just differentials.
Why not full again after 3 ?
i sometimes forced a new backup to see if it would create a full backup, but it always makes a differential.

See the images please, whats wrong ?

02-09-2023 22-55-17.png (20.03 KiB) Viewed 17933 times

02-09-2023 23-15-04.png (3.05 KiB) Viewed 17933 times

[cobian]

Ypou are keeping only one differential, so you never willbe upp to 3 differentials in order to change the backup to full.

[Lmgest]

LOL ...
Thanks