I have seen pictures where one timber framer was holding one square to the outside of the timber, another timber framer holding the other square tongue to tongue and using a combination square to check the mortise/housing.
I wanted to be able to do it alone, and not need the extra help....

I do see this tool as being something that we could use for measuring other things and used in other places....

I will be showing a local machine shop the drawings today, to see if they will give me a price....