I watched someone put their backpack in a sizer at a gate a couple of months ago. It was less than an inch over the personal item rule. The agent apologized, said no, and made her check the bag. She walked away frustrated. I walked away thinking about the data. That moment kicked off a small project. I pulled the published carry-on and personal item rules for 75 airlines and tested both. The carry-on data came out about how I expected: 14 of 75 airlines reject a standard 22 by 14 by 9 inch suitcase outright on at least one published dimension. The personal item data did not. 24 of 75 airlines do not publish personal item dimensions at all, including Delta, the largest US carrier. Among the 51 that do, the smallest published allowance is roughly one third the volume of the largest. How I tested The data lives in a JSON file on my server. 75 airlines, each with a carryOn object and a personalItem object.…