@GroundDead Yeah, dioptries are also written in decimal numbers, but without their " + " X (shortsight correction) or " -- " X (farsight correction) it is indeed confusing. About a way to make the difference (the more you know), you can assume that when a board is used like in this chapter, it...
@GroundDead - 1,5 means 15/10 in visual acuity ; 10/10 means that the person is able to distinguish two spots at a distance of 1/60 of a degree of each other, so approximatively 3 milimeters at 10 meters (yeah the eye is awesome) ; Therefore Komi-san can do the same at 15 meters