ᐅ Synchronous Mechanism of the Office Chair?

Hello,
I have been using an office chair for quite some time and recently came across a Stiftung Warentest review from 2007 where it scored well, particularly praising the synchro-tilt mechanism (simultaneous reclining of the backrest and seat).
The pictograms in the manual are not very clear about this, and I haven’t been able to figure it out yet. You can leave the backrest "flexible" or lock it, and also adjust the seat tilt separately. But how does the synchro-tilt work?
Does anyone have a tip on how to use it?
Thanks!

According to the instructions, the synchronization mechanism should be controlled by lever 7 and the response threshold adjusted using rotary knob 8, for example:

IKEA.de-manual.com/d-verksam-swivel-chair/Assembly-instruction.html

Best regards,
IKEA-Freund