0.6875 is basically a meaningless concept to me when I try to picture it in my head and what if you need to add it to another dimension? It’s not easy to work 4 decimal places in your head. .75 only works because I automatically convert it to 3/4. Maybe it’s just something that comes with experience but I don’t have trouble with knowing what’s what. If your not sure you can always make the denominator equal and figure it that way. 3/4=12/16 for instance. Easy math to do in your head.