I use a little purpose built laser. Very quick and easy. Place it on the rear sprocket and sight it up the top of the lower chain to the front sprocket. Perfect alignment.
You can get them in Oz now from
here. I have the cheaper dot version which is all you need. Just a miniscule rotation runs the dot the full length of the chain. I don't see any advantage in the more expensive version.
Actually I thought you saw it in action at OZBASM when we checked Benny's alignment after he got his new rear tyre.
