Sight adjustment tool for the Stgw-90 (also known as the SIG SG 550 and FASS 90) Swiss Army assault rifle is unique to the models developed for Grunig + Elmiger Swiss hunting and shooting sports equipment company initially by Wenger company (Wenger STGW 90), later by Victorinox company (Victorinox FASS 90).
It consists of two sub-tools for the rotating diopter drum rear sight adhustment (for higher/lower and right/left adjustment).
The right/left adjustment sub-tools seems to be the same for Wenger and Victorinox models.
But the higher/lower adjustment sub-tools have some difference in design (see photos).
The front scale of the knives has several markings that indicate how to use the sight adjustment tool.
Using the sight adjustment tool
Video on YouTube - Victorinox 'Korrekturmesser für Stgw 90' (SIG 550, FASS 90) usage.