Drift Method Chart

Watching a Star in the East
Star Drifts:Adjust Altitude:
NorthDown
SouthUp

Watching a Star in the South
Star Drifts:Turn Azimuth:
NorthClockwise
SouthCounterclockwise

Instructions

Roughly polar align with a polar alignment scope or by sight and start your clock drive.

Do a drift watch to the East:
1. Point the scope at a 2nd or 3rd magnitude star at about 20 degrees above the eastern horizon.
2. Put an illuminated reticle cross-hair eyepiece in the scope.
3. Move the scope back and forth in RA (East-West), turning the eyepiece until the star appears to move exactly parallel to one of the cross hairs.
4. Position the star on the RA cross hair so that it is exactly split in half.
5. Watch the star drift for 2 minutes.
6. Make a small correction in altitude according the the chart above.
7. Repeat steps 3-5.
8. Assess you progress. If the new drift is in the same direction, but worse, you corrected in the wrong direction. (Remember, North is not always "up" in the eyepiece). If the new drift is in the opposite direction, you've overcorrected, but you're on the right track. Keep following the chart.
9. Repeat steps 3-6, increasing the time until you get no drift over 5 minutes.

Do a drift watch to the South:
1. Point the scope at a 2nd or 3rd magnitude star at about 40 to 60 degrees above the southern horizon. Find something as close to South as you can (i.e. on the meridian). Slightly east of the meridian is better than west.
2. Proceed exactly as you did for the eastern drift test above, except do your adjustments in azimuth (not altitude) as directed by the chart.

Repeat the above procedures for new stars in the east and south until you achieve your desired accuracy. Typically, you will want to see absolutely no drift for 5 minutes.

This is assuming you are using a 12mm illuminated reticle eyepiece. If you are using a shorter focal length (higher power) eyepiece, or a 12mm with a barlow, you will achieve greater accuracy with the same drift time.

Finding a Test Star in the East

Finding a Test Star in the South