If you're looking for one, that appears to be a 1940s Lightning Portable Adding Machine with a Bakelite surface. Sometimes just called a Lightning Adding Machine.
This one in particular is one of the later 50s models that does direct subtraction. The earlier ones don't have the updated mechanism and you have to clear the unit to switch between subtraction and addition which makes them less useful for this.
Originally it would have come with an aluminum stylus but you could use a pen. It's not recommended to use a pencil because of the risk of breaking off graphite inside.
I personally use an old Nintendo DSi stylus I had lying around.