Cuz the older I get the less I'm able to follow a straight line!! Really, though, I paper piece a lot, probably more than I need to and even using a pencil line I tend to stray a little, especially at the end of the seam. I have lines taped on my machine bed, one that lines up with the needle and one that is 1.4" away to line up, but this laser would show the line all the way on top of the fabric (hard to understand, I know, but for $6.oo this is worth a try.) Here it is mounted on a saw.
http://www.harborfreight.com/laser-marker-93242.html
And my taped bed, I just follow the bottom corner or mark up the taped line:
Point to point
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at 1/4"
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