Absolute linear scales

The GUIs can be set to show absolute or commanded position.

Also, have a look in Halshow (or with Halmeter) and see what the PID command, feedback, error and output are. (If I am right to think that this is a servo system)

terkaa wrote:

[Do these help? It seems that my error is in pid.y.error... Approaching direction does not have an affect. Do I understand correctly that control sees this -0.0239 postion error and tries to move Y by outputting -0.00952 volts to Servo Amp but it does not move with that voltage?

Yes, exactly. With only a P-Gain term you can never actually get to the set point, it is a real-life example of Zeno's paradox Or maybe not exactly.
For some small error the output of a P-only controller will be too small to move the system. So you will always settle at that small error from the setpoint. (though it would normally be symmetrical for a horizontal axis)

That is why you need some I-term to integrate the small error over time until it becomes a big enough voltage to move that final little bit.

Add some Igain and you should see the error disappear Start with about P/10 and increase from there. Too much IGain will eventually give slow oscillations.