Text this: What does plate glass reveal about camera calibration?

  ______   _    _      _____    _____     _  _   
 /_   _// | || | ||   / ___//  |  ___||  | \| || 
 `-| |,-  | || | ||   \___ \\  | ||__    |  ' || 
   | ||   | \\_/ ||   /    //  | ||__    | .  || 
   |_||    \____//   /____//   |_____||  |_|\_|| 
   `-`'     `---`   `-----`    `-----`   `-` -`