The Adix Company's calculator is a simple device that does nothing more than add single digit numbers, up to a total of 999.  If one had a long column of numbers to add (such as in a ledger) the Adix could be used to add up all the rightmost (1's place) digits, write down the last digit of the sum, write down the amount to carry, clear the device and then start over with the 10's place digits.  

Maybe that helped some people, but it's hard to imagine that it sped things up for anyone who had to do it a lot.  Surely, after just a few repetitions of such a task one would have memorized all the sums of 1-digit numbers and be much faster doing it in one's head.  It makes me think that owning an Adix may have been more about status than usefulness.  It had to have been a luxury item in the early 1900s.

Still, the Adix is  techo-elegant and a clever little thing, measuring only 3.25" x 5.5" x 0.75!  And it's fun to use.  Note that the very act of pressing a key adds the key's value to the running total. In this regard, the Adix is similar to a Comptometer.  I also find it interesting that it was made to be used in the case, which has a notch cut out of the right front side so that the rightward-sliding, sawtoothed part of the mechanism located below the keys is free to travel.

The only usability flaw is that the clearing mechanism only zeros the two most significant digits.  Before pulling the clearing lever you have to press whatever key will sum to the next multiple of 10 so as to set the 1's digit to zero yourself!  And that means you have to be able to do the very mental math that the device would seem to have been built to make unnecessary.  

This one was non-functional when I bought it.  Pressing keys did nothing because the "drive rod" (which connects the keys to the rightmost gear) had become detached.  After reattaching it, I found that the clearing mechanism had become jammed because the clearing lever had somehow become stuck behind the part it was meant to press on.  But even after I prised it back into position, the unit over- and under-added, and didn't clear the middle digit.  After disassembly, re-alignment of some parts, cleaning and reassembly, it works beautifully.

This Adix is built on a steel frame, with brass gears and an aluminum plate covering the counter wheels.  You may find others of different composition.

There is a great description of some of the calculator's mechanics at