grooves or lines, allowing for an even larger number of items to be counted. Over even
more time, they grew into what is called an abacus, a device with a frame holding rods
with free-moving beads attached.What is an abacus?
An abacus (the plural being either abacuses or abaci) is one of the earliest counting
devices. The term comes from a Latin word with origins in the Greek words abaxor
abakon,meaning “tablet” or “table”; these words probably originated with the Semitic
word abq,or “sand.” The devices—originally made from wood but now usually includ-
ing plastic—perform arithmetic functions by manually sliding counters (usually beads
or discs) on rods or wires.
Contrary to popular belief, abaci were not truly calculators in the sense of the
word today. They were used only as mechanical aids for counting. The calculations
were done inside the user’s head, with the abacus helping the person keep track of
sums, subtractions, and carrying and borrowing numbers. (For more about carrying
348 and borrowing in arithmetic, see “Math Basics.”)
What are the oldest surviving counting boards?
T
o date, the oldest surviving counting board is the Salamis tablet. Discov-
ered in 1846 on the island of Salamis, it was once thought to be a gaming
board, but historians have since determined that the white marble slab was
actually used to count items. The tablet, which measures 59 inches (149 cen-
timeters) in length, 30 inches (75 centimeters) in width, and is 1.8 inches (4.5
centimeters) thick, was used by the Babylonians around 300 BCE. It contains
five groups of markings, with a set of five parallel lines equally divided by a
vertical line in the center; below that is a group of 11 parallel lines, all divided
by a perpendicular line.But this was not the only counting board of that time. After the Salamis
tablet was developed, the Romans brought out the Calculi and the hand-abacus
around 300 BCEto 500 CE. These counting boards were made of stone and metal.
One example of a Roman abacus had eight long and eight short grooves
arranged in a row; beads would slide into the grooves, indicating the counted
units. The longer grooves were marked I to indicate single units, X to indicate
tens, and so on up to millions; the shorter grooves were used to indicate multi-
ples of five (five units, five tens, and so on). There were also shorter grooves on
the right side of the abacus, which were probably used to indicate Roman ounces
and for certain weight measurements.