From its introduction in 1932 to 1936 when the Contax II was introduced, the Contax I was a work in progress. There are no fewer than six iterations based on external features only. This is actually an underestimate. There were also many non-visible internal changes such as the location and physical layout of how the angular displacement of the lens couples to the rangefinder system. Other changes were meant to make the rangefinder system stay within specifications better. Later versions actually provide better focusing feedback to the user. These were not small changes, and many of the still-working models are actually later revisions. These revisions were incorporated in the Contax II, a much more reliable camera that went through fewer versions.