"20 x 16 picture mount popularity contest !

The second of the two apertures for a 20 x 16 picture mount takes the popular A3 size print which is 420mms x 297mms . This makes the borders slightly uneven in the long side whereas with the typical 20 x 16 and a 16 x 12 aperture near symetry is possible.  Both apertures have there uses and the A3 is possibly the more used print size.