That specific gunsight was someone elses from probably War Birds that has been kept alive by sucessive genreations of poni fans. I simply cleaned it up for AH use, and gave the obvious marks actual Mil values based on a 512x512 mask 2pixel = 1Mil.
Thank Uptown for the initiative to breath another generation of life into a good poni gunsight. Remove the lines and place an 85Mil ring around the cross and you have the "Fixed Mode" ring and cross for the P51D's K14 gunsight. Thats about where the opening is in the four primary lines. 85Mil is the hold off for a 20 degree of travel path low E turn lead shot or the 100mph ring for the MkII gunsight in the spitfire.