3:5 and 1:5 soroban
Ancient abacuses used to have additional upper or lower beads, why? Some traditional techniques seem destined to make life with the abacus easier. This is especially true when it comes to division. Perhaps you are curious to learn them.
What is the limit of the abacus?
Modern 1:4 soroban and exercise sheet
The best and fastest (initial) approach to the abacus for the 21st century student.