Review on Enhancing Turntable Performance with Strobe Disc: Tests 33-1/3 RPM and 45 RPM Speeds by Danelle Gilson

If you're just buying this to align cartridges better have a magnifying glass and a good flashlight handy. It does the job, it's very accurate, but it's hard to see the details. It's not necessarily bad. To be honest I used a paper protractor that I printed out from the internet which worked just as well and was easier to see. After struggling with this, I lined up my cartridge with paper, then tried again and finally it lined up perfectly. So you might be interested in using both. You can use it as a final checkpoint.