1. Mechanical Calculators
At the beginning handle a mechanical counting device from an old electric meter or a speedometer. Playing with it and exploring it will occur by itself. This amazing change from nine to ten and viceversa! You see the principle, understand it and perhaps you get an idea to build some of that kind.
We leave it and look further, see the old mechanical helpers of times ago with understanding and respect - No, not the slide ruler, its sophisticated design leads us away from our goal. We want to go the path of "digital" counting and calculating.
But Abacus too is neglected, as it is -like paper and pencil- more an aid to the memory and not a calculating device - it is neither a calculating machine nor an antecessor to the computer!
move on