Vortex Optics Lo Pro 水平儀

Installed this without having to take my scope off the rifle, which saved me a lot of re-zeroing headache. The bubble is easy to see from my shooting position without blocking the sight picture.

Finally a bubble level that doesn't block my view through the scope; the low-profile design is perfect for staying mounted while still seeing your target clearly. It snapped right onto my scope without any hassle.

Fits snugly under my scope without blocking the view, which was my main worry. The bubble is easy to read even in low light, though the mounting screws could be a bit longer for thicker rails.