Roman Hand Abacus

(right most column eighths and Modern Roman Numerals on abacus)

Rails:

References: Roman Abacus, Roman unts of measurement. Brass early reproduction", and Early depiction from "Opera historic et philolgica, sacra et profana".
Note: Eighths can easily be represented on right side by combining by treating the three bottom beads as eighths and top bead as half.
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