You could go all out precise on star positions in a sketch, but how long do you want to spend on a piece.
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A sketch also is just an individual's perception and interpretation of what they see.
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There is a place for this degree of positioning though. As Ken says, if you are describing the position of a supernova in a galaxy, being accurate in your position placements can be very useful.
But there are much more accurate methods of
measuring angles that leave any guess work out of the equation. Any graduated eyepiece you use you need to make the necessary calculations for each individual scope's focal length, and then you need to apply these calculations to your piece. Something like a Nexus DSC unit takes all the guess work out of it, regardless of the scope you are using, particularly when you use the 600,000 click encoders with it.
For positioning just a few stars is what you want to do, a graduated eyepiece is fine. However, realise that most of these eyepieces are not of the highest quality, often being only fully coated rather than the better multicoated. Depending on your scope AND the lens design of the eyepiece, the may be a large amount of aberrations present that can render the image poor at best, useless at worst. And the apparent field of view of these eyepieces is also very small. They are not intended as a high quality visual eyepiece. The example Matt gives is such a piece. A kellner design (from the quoted AFOV and number of elements), nothing for keen visual observing or sketching.
Alex.