It's part of the metric system. A very easy and efficient way of measuring things. Most of the world caught on years ago.... ;-)
I just use the adjustable spacer between the axle and the frame as reference for alignment. For instance now the length is set to 2.8cm on both sides. Am I doing something wrong?
I always measure the best I can, then I spin the rear wheel a few times and watch the chain from behind to make sure it looks straight. It's not very scientific, but I've never had any alignment-related issues yet.
Hunky did not mark these bikes very well. I used a chain alignment tool to get it this close and the husky marks are not the same on both sides.