This is a clip-on, adjustable tool to assist in aligning the reticle of a scope. I had a couple of scopes that when level the reticle was slightly off-level. This affects the use of the BDC or Mil-Dots and throws accuracy off over distance when compensating for drop or windage. There are tools out there to correctly align the rotation of a scope but if your reticle is not level and plumb after aligning then this tool will help visually assist in getting it fine-tuned.

To use it you will need to place it as far away from the scope as your rail system allows and make sure the scope is zoomed all the way out. You may need to adjust eye relief and parallax to get a clear picture. It's easy to use and anyone can figure it out.

Make sure the PLA is not cooled too fast so as not to warp the vertical post. Allow the pieces to fully cool before removing them from the print bed to further resist warping/bending.