My family used to make the rounds of all the relatives in winter/spring. Saturday with X, Sunday with Y, kids would play, moms would yak - and my dad and the other dad would get the taxes done. Dad would bring along the 30-pound solid iron adding machine - probably a Burroughs Portable, with the side-handle.
I remember the adding machines where multiplication was sequential adding, and having to keep careful count! Also remember doing returns by hand when I first started out. I have always taught assistants on paper; as far as I'm concerned, they are not qualified to touch the software until they understand how the information flows from schedule to form.