I finally stopped guessing on box sizes after a $60 ruler mistake ate a Saturday
I bought one of those cheap cardboard scoring rulers for $12 at a shop in Reno, then burned $60 worth of corrugated sheet testing a tablet stand mockup that was 3/8 inch too narrow, so now I cut one test blank at the real dimension before I ever score a fold, and I'm wondering if anyone else keeps a scrap bin specifically for sizing checks.