I'm a canter, I let the rifle drift off center instead of holding it straight up and down. This causes accuracy problems of POI shift to the side you are canting to and to a lessor extent, lower. The further the target, the more pronounced the error.

I discovered this a few years ago at a different match, one of the coaches told me that I cant. "Can't what?" I said back, and he said "No, not words, you are letting your rifle drift off perpendicular to the left which is why your are missing left." Bottom line is he pointed out a flaw I was doing and told me to get a level of some sort that I could reference when holding the rifle. It was news to me as I thought I was holding level pretty good. Every guy thinks they are a born natural at 3 things, when reality is that they could probably use instruction for all of them: driving, shooting and screwing.

So I went out and got a level, low and behold he was right! What I thought was a nice level hold was off a good 3/4 to 1 bubble off center. My scores went up consistently across any match I shot holding the rifle and in prone as well. I put a bubble level on every rifle I used frequently.

Then I hit my 40's and my close in vision went to crap
It has gotten so bad I use different prescription strengths for reading and computer distances. One reason I like rifle over pistol is I can make up for this with the scope optics, dont need to wear prescription lenses when shooting, just regular safety glasses as I still see fine at distance. While I could still see the bubble, it was no longer a clear image while I was in the scope eye-box.

Saw a ad a few years ago for a round electronic LED level indicator that mounted to the back of the scope occular. It was bulky, and pretty much limited to the one scope you mounted it on as it was the same circumference as the ocular. Too much $ for an accessory I could only use on one rifle.

Ran across another ad for a picatinny rail mount LED level around Christmas last year. Since it was rail mounted, I could move it between rifles easily and it wasn't limited to just one scope. Told the wife and lo and behold lucked out and got one for Christmas!

This thing was a game changer for ME!!!!!! Keep in mind that I know I'm a canter and try to correct for it. The LRA is set up in my periphical vision of my shooting eye so that I can see the LEDS color without focusing on them, keeping my focus in the scope. Before with the mechanical liquid levels I'd check cant, adjust, then get in the scope and not make any further cant corrections. Now with the LEDs going I find that I start to cant a little, but am able to correct without losing sight picture.

IT's also a HUGE time saver when shooting strings of fire in time limited matches as I eliminate the need to look at a bubble level when switching targets. It has also helped my silhouette scores as I found out I cant a lot even after correcting before getting in the eye box I would start to drift.

It's a bit pricey ($189-229), but now I am using it on every rifle I take out of the safe as I swap it from one rifle's pic rail to the new rifle's pic rail. I consider it the second best equipment upgrade I have discovered in my lifetime. I consider it so essential I am going to get a second one as back up. I am not affiliated with LRA in any aspect other than being a customer.

https://www.longrangearms.com/

SWFA 3-15 with CANT indicator in vertical mount


Another SWFA 3-15 with CANT indicator in horizontal mount (upper scope ring half pic rail)


Athlon Cronos vertical mount