I have this vision issue. I'm cross eyed, and even with glasses on (I have four different pairs), I can't use rulers they way everyone else does. Things have to be in the correct positions for me to be able to see them. I can't just slap a ruler down and be accurate. Unfortunately, my Tonic trimmer does not line paper up the way I need for me to be consistent and accurate. Accurate isn't as important as consistent. But since I can't always see what I'm doing, I am sometimes accurate and sometimes a bit off. Sigh.
When cutting large things, accuracy isn't as critical, but for things like inchies, it makes a difference. I don't do inchies if I can avoid them. Last night, I couldn't avoid them. It took me for-blinking-ever, but I got 144 one inch squares cut with very little error. I'd rather not have to do that again, but it's nice to know that I can.
When I get new cutting tools, one of the things I should do is to line up scrap paper with the marks and make a set of practice cuts. Then carefully measure what I've cut. That way, I can tell if I need to line things up with the right edge of the marked line, with the left edge of the marked line or smack dab down the middle of it. I've had my tonic for about a month now and I still haven't done this. Perhaps now would be a good time.