Drift Align
Drift alignment is a well-known technique for achieving polar alignment and is considered by many to be the "gold standard". The Drift Alignment tool is a "wizard-like" sequence of dialogs that can help you work through the drift alignment process and get quantifiable results. Once you've calibrated your guider, click on 'Drift Align' under the 'Tools' menu. The first Drift Align dialog will appear to help you adjust the azimuth on your mount. If you are using an ASCOM mount, you'll have the option of slewing to an area near the celestial equator and the celestial meridian. If you're not using an ASCOM mount, you'll need to slew to that location manually. Once the scope is positioned and you have a suitable star in the field of view, click on the 'Drift' button to begin collecting data. You'll see the graph window with a display of star deflections and corrections and, more importantly, two trendlines. When the mount is precisely polar aligned in azimuth, the Declination trend line will be perfectly horizontal. Let the exposures continue until the declination trendline has stabilized and is no longer jumping around with each new exposure. At the bottom of the graph window, you'll see a measurement for the polar alignment error in azimuth. And, in the image window, you will see a magenta circle around the guide star. The circle indicates an upper limit on how far the guide star needs to move when azimuth is adjusted. (Initially, the circle may be too large to be visible on the screen, so you may not see it until your alignment gets closer.)
Now click on the 'Adjust' button to halt guiding, then make a mechanical adjustment in azimuth. Watch the guide star as you make the adjustment, moving the guide star towards the magenta circle, but not beyond it. Once done, click on the 'drift' button again to repeat the measurement. If your adjustment was in the right direction and did not over-shoot, the Declination trendline will be closer to horizontal. Continue iterating in this way until you are satisfied with your azimuth accuracy. You can use the 'notes' field to record which way the drift line moves depending on how you make the adjustment. For example, you might note that a counter-clockwise turn of the mount azimuth knob moves the drift line "up." Since these notes are retained across PHD2 sessions, subsequent drift alignments will probably proceed more quickly.
Until you are experienced with drift aligning your particular mount, the 'adjustment' part of the process can be a bit tedious. At first, you'll have to determine how to adjust a knob on the mount to achieve the desired effect: "how much" and "what direction." To help with this, the PHD2 drift align tool supports "bookmarks". These are a handy way to record the positions of the guide star before and after you've made an adjustment. Bookmarks are accessed using the Bookmarks menu, or keyboard shortcuts, as follows:
b : toggle/show bookmarks
Shift-b : set a bookark at the current guide star position (the "lock position")
Ctrl-b : clear all bookmarks
Ctrl-click somewhere on the image: set a bookmark at that position, or remove the bookmark that's already there
By setting a bookmark before you make a mount adjustment, you can get a clear view of how the adjustment has moved the star on the guide frame.
Next, click on the 'Altitude' button. Then slew the scope to a position near the celestial equator and 25-30 degrees above the horizon. Click on the 'drift' button to begin collecting data for the altitude part of the alignment process. As before, you will iterate between making adjustments and measuring your alignment until you are satisfied with the result, keeping notes as you go about how mount adjustments affect the behavior of the declination drift line. If you make substantial adjustments in altitude, you'll need to go back to the 'azimuth' measurement and repeat that procedure. If you work through these procedures systematically, you'll converge on a good polar alignment with a known degree of accuracy. A good polar alignment will help your guiding performance, especially in declination.
The drift alignment tool is easiest to use when you are using an ASCOM connection to your mount (including an 'Aux' connection). Even if you subsequently want to use ST-4 style guiding, you should use the ASCOM connection for drift alignment. If you can't do that for some reason, the following features will be impaired:
Scope position data and slewing functions will not be available - you'll have to slew the scope yourself
The magenta circle that identifies the "target" for moving the star will be inaccurate and will be displayed as a dashed line. This dashed circle will identify only an upper bound to the adjustment, so you will probably want to make smaller adjustments to avoid over-shooting.
A very complete step-by-step tutorial for drift alignment is available on the Openphdguiding web site, and first-time users are strongly encouraged to study it. (https://sites.google.com/site/openphdguiding/phd2-drift-alignment)
Lock Positions
PHD2 normally sets a 'lock position' where the guide star is located at the end of calibration. Depending on the details of the calibration sequence, this may not be exactly where the star was located at the start of calibration - it could be off by a few pixels. If you are trying to precisely center your target, you may want to use a 'sticky lock position.' You do this by clicking on your guide star before calibration, then setting the 'Sticky Lock Position' under the 'Tools' menu. After calibration is complete, PHD2 will continue to move the mount until the star is located at the sticky lock position. So you may see an additional delay after the calibration while PHD2 repositions the scope at guide speed. The sticky lock position will continue to be used even as guiding is stopped and subsequently resumed. Again, this insures a rigorous positioning of the guide star (and presumably your image target) at the expense of delays needed for PHD2 to reposition the mount.