[jlightfire]

Hanging a curtain rail that is centered both vertically and horizontally between the window and the ceiling, and it is leveled (with a bubble level), while in a ladder. Mark and then drill. It is harder than it seems at first. Maybe I'm just too a computer guy.

[tedapeters]

Especially when ceiling drywall often is not perfectly straight (the line between wall and ceiling often has dips)