Imaging with a 2 axis equatorial platform and small Dobsonian telescope

[Imager57]

I'm new to imaging and have been experimenting recently with imaging. I've succesfully made an equatorial platform for visual use with Dobsonian telescopes and now I'm trying to add a second axis for guided imaging. I tested the protype I've been working on last night and got what looks like some good 4 minute guided exposures of star fields.

The guidng software I'm using is PHD2, just wondering if I can get some basic help with it from someone who has experience. This is the calibration graph of my calibration last night. Wondering how good it is and what, if anything could be improved. Would appreciate any help from experienced imagers. Thanks!