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Great picture, Jakob -- and a good first attempt at using PHD2. I'll explain what's happening in the graph there.
The lines on the graph show you a few things:
1. The amount of error in your guiding, both in Declination (Red) and Right Ascension (Blue). This is indicated by how far the blue and red lines deviate from the center line (0). The value given for the amount of error is in arcseconds. If you prefer to see the size of the guiding error expressed in pixels, you can change it via the Settings button the left.
2. The direction in which the error occurred. This is indicated by whether the red or blue line deviates up or down from the center line.
3. The amount of adjustment that PHD is making (via guiding pulse to your mount) to correct that error. These corrections are indicated by the red and blue vertical bars which extend away from the center line in the opposite direction from the error to which they correspond.
Ideal guiding with an accurate polar alignment, by contrast, would have the red and blue lines close to the center (0) and few correction bars. If corrections have to be made, the smaller those bars are, the better.
In the graph you've provided, your guiding is showing an RA Oscillation value (shown in red down the bottom) of 0.07. Generally speaking, when this number is showing as red it's not a good thing. You want to aim for a value as close to 0.50 as possible. But at short focal lengths you can get away with less-than-perfect values on your graph, especially if you're binning your images. It all comes down to how much you want to get out of your imaging.
To give you an idea of how the values on your graph translate to impact on your image quality, consider the following.
Your D7000 camera has a pixel size of 4.78µ, which on your scope translates to 1.792 arcseconds per pixel. As soon as your RMS Errors in PHD2 exceed a quarter of that value -- 0.448 arcseconds -- shift is introduced into your image. This is not including image artifacts caused by circumstances such as mechanical imperfections in your mount or atmospheric seeing conditions.
You might wish to increase the delay between guiding camera exposure times so that your mount is making fewer corrections. Depending on the brightness of your guide star, 3-4 seconds is a good value.
Hope this helps!
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