A head roughly 10 inches from top to chin supplies the opening scale reference. HMS Dreadnought's 12-inch gun then gives the first naval calibre, with a bore one foot across. The comparison establishes the scale for the larger gun diameters that follow.
Notable Point · 0:00-0:32
HMS Dreadnought's 12-inch starting point
HMS Dreadnought's 12-inch bore is compared with a head roughly 10 inches from top to chin.