The NexStar User's Guide II - Excerpt from Chapter 6
Slew at Slow Speeds
This feature allows you to exchange the directions of the up/down or left/right arrow buttons when manually slewing at slower rates with the arrow buttons. This provides better control when using the scope with different combinations of visual and photographic accessories. For example, perhaps you connect a small video camera to the visual back of your SCT telescope and then connect this to a video monitor to give a group of spectators a view of the moon. You may find that you need to reverse both left/right and up/down. When using a diagonal in an SCT or refractor, you will find reversing the up and down buttons provides more natural control.
If you change these settings, remember to reverse the applicable arrow buttons when centering stars during the alignment process.