> If a basic customary unit of length is an inch, many people can put two fingers together and estimate that on the human scale. But who can estimate or eyeball

> If a basic customary unit of length is an inch, many people can put two fingers together and estimate that on the human scale. But who can estimate or eyeball a millimeter? If you'd grown with a metric system you could eyeball a centimeter with ease. Also comparing orders of magnitude different measures for estimation isn't fair, how precise would be your guess of a barleycorn?