If you have never used a Retina camera before there are a few things that you need to be aware of or it may be a frustrating business for you.
The "modern" folding Retina cameras, models Ia, IIa, Ib, IIc, IIIc etc. all share one common feature, the frame counter counts backwards, from whatever you have set it to, down to number 1. Now that, in itself is not all that unusual, but the Retina adds a new twist. When the counter reaches the number 1 the film advance lever is locked. This is a feature said by some to have been designed in by Kodak to prevent users from getting that extra exposure or two from the film, but is likely to have been mainly added to stop rough users from tearing sprocket holes on the film by forcing the film advance when the end of the film has been reached.
Many Retina cameras are believed to be faulty by people who are unfamiliar with them when the shutter seemingly doesn't fire and/or the film advance doesn't work. In reality the frame counter has reached number 1, and as a consequence, the film advance has locked. In this case the frame counter just needs resetting to free the film advance lever.
On the Retina Ia and IIa the frame counter (highlighted with a red arrow below) is reset by simply turning it in the direction of the engraved arrow on the top. Do not turn it the other way, you will just break it.
On the Retina Ib, IIc, IIIc the frame counter is reset by moving the frame counter forward by repeatedly pushing the chrome button on the back of the top housing in the direction of the arrow while holding the film release button down.
Another "useful" feature to be aware of, is that with the folding Retina cameras you must set the focus back to the "infinity" position in order to be able to depress the front lock buttons at top and bottom of the shutter housing to close the front cover. The position of the upper and lower buttons are indicated by the red arrows in this picture below.
