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Picture of how to make a knex abacus/soraban
This is the abacus/soraban I made a few days ago. It works well, and I like it.

Step 1:

PARTS LIST.
21 green rods
8 white rods
8 yellow rods
36 gray 4 slot connectors
6 blue 7 slot connectors
8 blue spacers
32 gray spacers