Sur le site, il y a trois pages sur le MB3 (cliquer sur Next en bas de page).
Extrait à propos du compteur :
"Frame Counter
The frame counter on the motor drive shows the number of unexposed frames remaining on a roll of film. It is calibrated in even numbers from 0 to 40. The frame counter preset wheel can be rotated in either direction. When the counter reaches zero, the motor will stop automatically.
If you want a certain number of frames to be set for continuous firing, just set the counter to the desired number. This operation can be done repeatedly. The frame counter on the camera also continues to operate when the motor drive is attached, so you can easily see how many exposures you have left.
Be careful to set the number of frames correctly. If you overestimate the number remaining on a roll of film) the result may be that the motor will pull the film off the supply spool or damage its perforated edges, since the motor will continue to operate until the counter reaches zero.
Turning the frame counter's preset wheel away from its zero position when the motor drive is removed from the camera may occasionally result in the motor drive running freely until the counter resets itself to zero.
This is a normal operating condition, caused by the end of the film being reached before the motor drive completes its advance cycle, and is no case for concern. When the motor drive is reattached to the camera, this condition will be corrected automatically.
The motor will not operate when the counter is at zero. Always check the counter before starting to shoot, especially at the beginning of a roll."