The No. 0 Brownie is the smallest in the Brownie camera range. It took 8 photos of 1-5/8 x 2-1/2 inch (4,1 x 6,3 cm) on a roll of film. The size of the camera is 2-5/8 x 3-3/8 x 4-1/8 inch (6,5 x 8,7 x 10,4 cm).
The size of the photos is the same as the very popular Vest Pocket Kodak size. The VPK was introduced in 1912 and was an immediate succes. So Eastman Kodak saw its chance and produced a box camera that took the same size of pictures. The VPK did cost $ 6 while the No. 0 Brownie did cost only $ 1.25. in the early years and $ 2.00 in the late 1920's.
The VPK is a folding camera that has to be expanded before it can be used. When not expanded properly the photos will not be in focus. With the rigid box No. 0 Brownie there is no risk of incorrect focus.
There are a number of small design changes that were made over the years:
July 1917: the film tension springs bearing on the ends of the spool instead of the center of the spool. A direction arrow was added to the winding key plate. About 1928: double crossed line on the front was replaced by double rectangles.
French instruction manual
Sample of a photo that was taken with a No. 0 Brownie. The album page with this photo was sold on eBay but is unfortunately not in my collection.