Three lines above, the letters have twice the dimensions of those on the 20/20 line. The chart is at a distance of 20 ft, but a person with normal acuity could be expected to read these letters at a distance of 40 ft. This line is designated by the ratio 20/40. If this is the smallest line a person can read, the person's acuity is "20/40," meaning in a very rough kind of way that this person needs to approach to a distance of 20 ft to read letters that a person with normal acuity could read at 40 ft. In an even more approximate manner, this person could be said to have "half" the normal acuity.