The FAT Wrench & mini-levels are (cheap) necessities, and I've found this one here to be great for keeping the rifle level during the process... https://www.midwayusa.com/product/537916/ctk-precision-all-purpose-gun-level Couple other thoughts I hadn't seen mentioned yet are related to scope-mounted levels, uniqueness of body shape related to positioning & scope cant, and a process for fine-tuning the scope level. I start off with leveling scope-to-rifle using methods stated previously, but once that's done, use a Plum Bob with a neon-bright line hanging a reasonable distance away (~50y +/-, depending on scope) to set a scope-mounted level as true as possible to both reticle and gravity. (after waiting for line to stabilize) Then - depending on the platform/stock, how it sits in the shoulder (from standing/kneeling/prone), and how close-to-true the original rifle-to-scope leveling is, will adjust scope cant in rings as needed to maintain scope level with rifle/natural point of aim (rifle alignment being secondary). This is super easy given the pre-calibrated scope-mounted level; sometimes no adjustment is needed, sometimes it is... Here's one I like: https://flatlineops.com/products/levels/recon-34mm The reasons for these extra steps is that: 1. Rifle cant is largely irrelevant outside of maintaining reasonable vertical alignment of the scope/bore centers - what really matters is proper level/alignment of the reticle with gravity (assuming a quality/functional reticle). 2. Small errors in scope/reticle leveling turn into big misses at-range (if you're never shooting past ~100-200y, this isn't so much of a concern). 3. Various stocks/profiles will fit-up differently, impacting natural-point-of-aim considerations, and this approach helps to accommodate for keeping a level reticle without having to "muscle-it".