Chair Verksam Synchronmechanik?

Hello,
I have been using a chair for a long time and recently happened to read the Stiftung Warentest (from 2007) where it scores well and especially the synchron mechanism is praised (simultaneous tilting of backrest and seat).
This is not clear from the pictograms in the manual, and so I have not been able to do it yet. You can leave the backrests "flexible" or lock them, and also adjust the seat tilt separately. But synchron mechanism?
Does anyone have a tip on how to do this?
Thanks!

According to the instructions, the synchronization mechanism should be controlled via 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 friend