When sound was adopted in cinema towards the end of the 1920's, the soundtrack was inserted in the area of the frame, occupying about 2.5 mm on the left. In this way, the projectable area was reduced to a 19 x 22 mm gauge. This almost square gauge was used for a couple of years, until it was decided to adopt a new standard that brought back the 1 to 1.33 ratio.
This gauge, also called Academy aperture has been practically the only one to be used in 35 mm copies of sound film and continues to be one of the most used formats because it practically corresponds to the television gauge in use today.