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.
Since the resolution determines the size of a pixel it can also be used to modify the size of the overall image. As an example consider one bitmap which is 200 pixels horizontally and 100 pixels vertically. If this bitmap was printed at 100DPI then it would measure 2 inches by 1 inch.