Here are two retractable tape measures. The one on the left is a classic by Stanley, the other, made by Panyi, clearly a cheaper clone. Looks the same, works the same… except for one small difference.
Notice the difference?
This type of tape measure has a stated offset printed on it, equal to the width of its metal case, to allow taking inner measurements. In the Stanley unit, the number is +50 mm, a clean round number that’s easy to add to the number you read on the tape. I also have a Stanley tape of different design that uses +60 mm… again, a nice round number.
But the cheap knock-off uses +55 mm – far less easy to rapidly add in your head. Couldn’t the manufacturer bother to add or subtract 5 mm to the case size?…
Bad, bad designer!