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.
If one has a right angle, and knows at least one other angle, he subtracts it from 90 to get the other angle. Here's another way to measure angles: use the fist! If one makes a fist, and extends the arm straight, the area covered by the fist equals 10 degrees. One can make rough estimates of angular elevation in this way when hiking or looking at the night sky.