Abacus with 20 balls
red / blue
Sloped and therefore very stable design with stainless steel rods.
Balls (Ø 1.3cm) and frame of RE-Wood®. (25 x 4.5 x 6cm)
All sorts of things can be done with the red and blue balls arranged in steps of 5: Numbers can be represented or simply counted, "greater than, equal to, or less than" comparisons, all basic arithmetic operations , tens transitions, drawing square and cube roots, and much more.