I had one of these! Got it at a yard sale when I was eighteen.
If I recall correctly, you put it on and snap up the front and back, then have someone pull the bottom down as hard as possible, which starts to f...... What is the name of the dress form? I've been trying to find one just because I like vintage sewing stuff, but I don't remember the name of it. I thought it was My Double, but when I google that I get a different type of dress form.
The box is labled "My Double" Dress Form From Dritz. But the modern version that Dritz has is also call My Double so it just gives you all the modern ones. Thanks for the details. It will help a lot.