NuTone Intercom Photo Gallery > NuTone Chime Modules > NuTone IA29 layout
The 3 red boxes show the following.
1. The 4 wire connection screws: Common, Front, Rear, Side inside the box at the top of the picture.
2. Bottom left box shows yet another style of ribbon wire termination on this IA29.
3. Another volume adjustment control wheel, in a completely different location than the other 2 I showed.