Usually units like that are used because they make the scale easier to grok. Unfortunately, with large numbers, humans fail to truly understand the scale betwee

Usually units like that are used because they make the scale easier to grok. Unfortunately, with large numbers, humans fail to truly understand the scale between them (e.g.: you can innately feel the difference between one and a thousand more easily than between a quadrillion and a quintillion). This is also the reason why you'd prefer eating dots in Pac-Man to give you 100 points a piece rather than 1 million. Thus, having to say "1/10000" defeats much of the point of using the width of a human hair as a unit. I don't think it's much harder to innately grasp 5 nanometers than 1/10000 the width of a human hair.