Correct, that's the one.
Yes, when adjusted, you secure the plate with two more vertical knobs from beneath the plate and it is steady.
Yes, the two X knobs provides the rotation.
I also have a technoprint printer, and the two X adjustments are much better engineered. But I don't like it for other reasons.
They solved the problem with adding a spring which provides tension in the opposite direction (the moving plate is always pulled in one direction).
I attached a sketch according to my memory. You can see the gaps. When you start turning the knob in the opposite direction, the blue circular end tap (which fitted on the screw end), has to move "all the way" through the gap and then finally touch the plate before it finally can press against the plate and move it.
So, imagine you aligned it too much to the left, then you must turn the knob in the opposite direction "a lot" to fill the gap before the plate actually moves to the right...