I really like this: https://www.shortactionprecision.com...c-level-system

I was a bad canter, with this I can see it in my peripheral vision as a color so I don't have to focus on it and lose sight picture. It has helped my basic fundamentals tremendously in keeping the rifle level now. It's pricey, but you can swap it easily among any pic railed guns. I had trouble focusing on the mechanical bubble style levels at short distance (cant focus eyes that close without glasses) and they took a lot more time between shots, the Send IT is so much easier and faster.