The Accu/Level Scope level attaches to the scope tube to give the shooter a visual verification that the rifle is dead level before each shot. This helps eliminate inconsistent grouping that results from inadvertently canting the gun. This normally isn’t noticeable at shorter ranges, but can have a significant negative effect on group sizes at long range. The Fixed Accu/Level is designed to be aligned with the gun during installation. Works for both right-and-left-handed shooters.
Big Book Catalog, Issue:67, Page:282
Sinclair, Issue:4A, Page:209