Boys start to get acne at the age of approximately 12 years, with a range of 9 to 15 years old. As most girls will attest, boys on average mature later than girls. Early on in the onset of teen acne, the main lesions are blackheads and whiteheads.
The angular size (angular diameter, apparent size) of an object as seen from a given point is the visual diameter of the object measured as an angle. The visual diameter is the diameter of the perspective projection of the object on a plane through its center that is perpendicular to the viewing direction.
So a person with 20/10 vision would use the calculation: which gives a result of .5 arc minutes. For a person with 20/10 vision (or .5 arc minutes), this translates to .000145444 radians. With the angular resolution in radians, we can then determine the pixel pitch you are able to see at a set distance. To do this, we need to use part of SOHCAHTOA: