When you have two telescope fixed mounted together ( One for guiding. ) it is often difficult to find a suitable star for guiding. When you move the telescope to the nearest star in the field the object you want to record on a CCD camera often moves out of the CCD chip. The oculars used conventionally for guiding gives rather high power in order to guide accurately with few or none stars in the field. This was now a problem for me and I thought about how convenient it could be to have a low power ocular with lots of stars in the field with which I could use for guiding too.
As an old maker of telescope mirrors I suddenly realized that the visual outer limb ( edge ) in the ocular field could be used for guiding,. ( If there is a star close to center I use the conventional method with ocular with cross hair. ) This I had to try. I put a star close to the limb and adjusted the R.A. drive so that it almost disappeared out of the low power field. I then easily could keep the star exactly on the limb and guided. This worked better than I could imagine and I named it The Knife Edge Method inspired by the Foucault Test device used in mirror making. The guide star disappeared and reappeared and I balanced the star on the limb.
Now I obviously prefer this method because I can use 32 - 55 mm oculars to guide with instead of the narrow 12mm cross hair ocular.

Adjust your polar axis accurate enough for running 3 - 5 minutes without correction in declination. You can use a sector of at least 80 degrees on the eastern or western limb. Of course moving comets can make some problems.