I was given the Polaris alignment protractor when I bought a Nottingham dais new. It was easier to understand than the db systems one I also have. I used it on a horizon as well as the dais and it works good
http://www.russandrews.com/product-Polaris-Cartridge-Protractor-5040.htm
http://www.russandrews.com/product-Polaris-Cartridge-Protractor-5040.htm