[There is a downloadable PDF version of this tutorial available here. Thank you Doug Duncan - Andy]
The drift align tool in PHD2 can be used to quickly obtain a precise polar alignment of your equatorial mount. The process takes a little bit of practice, but after doing it a few times, you should be able to obtain an accurate polar alignment in minutes.
You will see a window like this:
Position your scope for the Azimuth axis adjustment. Point near the Meridian and the celestial equator. You can either click the Slew button, or move the mount manually. Your scope should now be pointing something like this
You are going to alternate between measuring the error (Drift), and adjusting the mount (Adjust). The rate of declination drift tells us the amount of alignment error. Each adjustment will reduce the error, and you repeat the process as many times as you need to get the error close to zero.
Click Drift to start measuring the declination drift. PHD2 will select a guide star and start guiding. After a few moments you should see something like this:
Pay particular attention to the Declination trend line (Red). At first the Dec trend line will be jumping up and down, but soon the noise should "average out" and the slope of the line will become somewhat stable. When that happens you are ready to adjust the mount's Azimuth.
Our goal is to make the Dec trend line "flat" -- neither trending up nor down over time. By adjusting the mount's azimuth, you will change the slope of the Dec trend line.
If this is your first time adjusting Azimuth, you will not know which way to go--East or West? PHD2 does not know either, so you just have to guess, and you have a 50-50 chance of getting it right. If you choose correctly, the new drift line will be flatter (less steep, closer to horizontal) If you choose incorrectly, the drift rate will increase (more steeply downward in the example above.)
Click the Adjust button. PHD2 will stop guiding, and you can make your adjustment. You'll see something like this
After moving the guide star, click Drift to make another measurement. Before you click Drift, it's OK to nudge the mount to re-center the star, or to find a different star, or to get back closer to the meridian. Also, you can choose your own guide star by clicking on it, or just let PHD2 choose.
After a short time drifting, you will have another Dec trend line. Did it get better (closer to horizontal) or worse (away from horizontal)? Make a note to yourself in the "Azimuth adjustment notes" area of describing how you adjusted azimuth, and which direction the Dec slope moved. You can use this information next time you drift align so you do not have to guess which way to make the azimuth adjustment. For example, with my setup, turning the azimuth knob clockwise makes the slope go down. Having the note there reminds me that I need to turn the azimuth knob counter-clockwise to make the slope go up.
Repeat the measurement and adjustment of the mount until you achieve a good flat horizontal dec trend line, like this:
Now, you will need to repeat the process for the mount's Altitude adjustment. Click the Altitude button; the Drift tool will now look like this:
The exact position is not important, but 25-35 degrees above the horizon works well.
Click Drift to start drifting.
Drift until you have a stable Dec slope. Click Adjust, then turn the mount's Altitude adjustment knob. Use your notes recorded in the "Altitude adjustment notes" area from a previous session to determine which way to turn the knob to move the slope in the desired direction. For example, with my setup I turn the altitude knob clockwise to make the slope go "down".
Just as with the Azimuth adjustment, repeat cycles of Drift and Adjust making the measurements and moving the guide star to the magenta circle. Again, the goal is to get the dec drift line to be horizontal.