Hi Ronny,
I would stick with PHD2 for the moment, if you get your head around Peter's comment you could/should investigate alternatives (Metaguide is
http://http://www.astrogeeks.com/Bliss/MetaGuide/ ).
I am not a PHD2 expert, but I made a screen shot of the 'History'. To view this window select 'Display Graph' in the main 'View' drop down menu (unfortunately the naming and labeling is not consistent).
Then you can set the 'y-axis units' in the 'Settings' drop down on the left. The options are 'Arc-seconds' and 'Pixels'.
When in 'Arc-seconds', and you have provided the guide scope focal length (brain - Global) and guider ccd pixel size in micrometers (brain - Camera), it will represent physical pointing error of the guide scope/camera. Assuming the rigid connection of the guide scope to the main scope then this will represent the pointing error of the main scope as well.
If in 'Pixels' it will show the guide star movement on the guide ccd. It can be handy for trouble shooting (say for calibration see if the star moves with the cal steps), but it has no real representation and you can't compare guide performance because it depends on the focal length and pixel size on how much the scope is moving. This actually comes back to Peter's comment.
Oh, yes I assume you have a wedge
Hope this helps.
cheers,
Bram