This is an early version of the Hasselblad film back, often referred to simply as the 12 magazine. It predates the A12 Automatic series you logged earlier. While the A12 automatically stops at the first frame during loading, this older manual version requires the photographer to use the folding crank and look through the small circular peep-hole on the back to align the number 1 printed on the film's paper backing. Once set, the mechanical counter takes over.