I SO want a Curta for my very own! What a delightful object...The Curta is a marvel, wish I could afford one. (I collect old calculating gear.) Curt Herzstark invented it while a prisoner in Buchenwald concentration camp. When WWII ended he had Contina AG of Luxembourg manufacture them, and they kept making them until 1970. I know of nothing else similar. Magnificent piece of design and engineering.
We do have one in our computer museum collection, of which I'm (acting) president.
For those who don't know, a Curta looks like this:
As to the calculator/computer divide, it would probably be reasonable to define the computer as a general-purpose calculator in which you could store and make it perform a program of steps, including control of the sequence of those steps, i.e. it performs an algorithm. Whereas, a calculator operates by means of an external action (you put stuff in by hand, and you manage the algorithm, not the calculator).