Kodak Numbering Early folding Kodaks used film determined by the camera number. The Number related to the image size - the smaller the number the smaller the image, This system was replaced by the more familiar (though now largely extinct) three digit system. Just to add amusement for collectors a century later, the Folding Brownies don't qualify.

Camera/film No.	Year Introduced	Frame Size
No.0	1902	1.5/8 x 2.1/2"
No.1	1897	2.1/4 x 3.1/4"
No.1A	1900	2.1/2 x 4.1/4"
No.2	1899	3.1/4 x 3.1/4"
No.2C	1916	2.7/8 x 4.7/8"
No.3	1900	3.1/4 x 4.1/4"
No.3A	1903	3.1/4 x 5.1/2"
No.4	1908	4 x 5"
No.4A	1906	4.1/4 x 6.1/2"