In this and other videos, you may see a "wobble" in the Impress cone as it turns upward and downward. That is normal. The Impress has a ball bearing swivel inside the cone that allows it to align perfectly when it contacts the tubing. You'll see it self-align when it makes contact. Thanks Francesca!
http://www.youtube.com/watch?v=WlwKLUTLYV4

In this video, the author is using a plastic-jawed caliper, and a felt tip pen to measure and mark her tubing. I recommend use of a digital steel-jawed caliper, so you can accurately and simply mark your tubing length by scribing a mark with the tip of the caliper jaw. See the instructional article "Lining Beads With the Impress" for more tips on measuring and cutting.
Thanks Heather!
http://www.youtube.com/watch?v=T0BUn55TXm8