Roman Hand Abacus

right most column twelfths and ancient Roman Numerals in display


Alt Roman Hand Abacus

right most column eighths and modern Roman Numerals on abacus


Russian Schoty


Georgian Schoty (not to be taken seriously)


Danish School Abacus


Mesoamerican Nepohualtzintzin (similar to Japanese Soroban base 20)


Babylonian Watch (proposed by author)


Chinese solid-and-broken-bar system


Base 16 Abacus


ABACUS Guide Book.
Manual for xabacus (similar X program).
Java Source: abacus.zip.