A multi-viewing attachment is one of the most useful accessories that you can get for a microscope. It can also be one of the most frustrating. A multi-viewing attachment allows from two to more than eighteen people to see the same image.
Most makers design there systems to be at their best when used by two to six viewers.
A.O. has been the driving force in multi-viewing. The first multi-viewing attachment was the dual head accessory. This allowed two people to sit at the same microscope facing each other. This worked well but it was very difficult for the users. They were both draped over the microscope playing kneesies with each other.