On really old gravestones, my best example is an 1830 sedimentary sandstone, Many 3s on the gravestones look like 5s when you are just standing in front of the gravestone looking at it. It was only when I took close-up photos and studied the numbers carefully that I discoved this problem. Once you study the close-ups, it is easy to see the difference. But looking at the stone under ordinary conditions , most of the 3's look like 5's.