The Sniper laser chain aligner makes the task of ensuring your sprockets are perfectly aligned a snap. You simply clip the tool onto the rear sprocket, and it shines a laser point at the front sprocket. When the dot is in the middle of the front sprocket teeth, you're done!
It's a very handy device to have in your toolkit, especially if you run a clutch which has a bit of end float. It's much easier to get the sprocket in the middle of the float range when you're not flopping a straight edge around.