The human eye is able to determine the relative position of objects with amazing accuracy, up to 3-5 arc seconds. An interesting fact is known: in April 1984, Dr. Dennis M. Levy of the Optometric College of the University of Houston, Texas, USA, several times determined the position of a thin white line with an accuracy of 0.85 arc seconds. It's like noticing a 6 mm displacement of an object from a distance of 1.6 km.
It is interesting that without the help of optical instruments, under the best viewing conditions, in good lighting, human eyes can distinguish 10 million different color shades. The most accurate electrical spectrophotometer has an accuracy of only 40% of that of the eye. About 7.5% of men and 0.1% of women do not distinguish colors at all. The extreme form of color vision impairment - monochromatic vision - is very rare. The highest percentage of people who do not distinguish green from red is observed in Czechoslovakia, the lowest among Fijians and Brazilian Indians.