The Stephenson Abacus™ is a counting-board type abacus with a particular structure and a set of methods to perform addition, subtraction, multiplication, and division on decimal (base-10) or sexagesimal (base-60) place-value numbers in the form ± c × b ± p.
Without violating the methods of operation, the parameter ranges for base-10 arithmetic are: 0.00000001 ≤ c ≤ 99.99999999, b = 10, and 0 ≤ p ≤ 9,999. For base-60 arithmetic they are: (0,0;0,0,0,1) ≤ c ≤ (59;59 59 59 59), b = 60, and 0 ≤ p ≤ (59 59;).
The Stephenson Abacus™ can be used to do any modern engineering calculation without knowing or referring to addition or multiplication tables. If ancient peoples used The Stephenson Abacus™, it would have been their supercomputer.
The Stephenson Abacus™ may today be an inexpensive and useful tool to:- teach place value and the basis for the standard algorithms used to perform all four arithmetic operations;
- teach an appreciation of ancient numerology (Roman, Greek, Egyptian, and Babylonian) by associating ancient number symbols with the lines on The Stephenson Abacus™;
- foster an interest in math history; and
- provide scholars with a robust working model of what could be done with counting-board type abaci so that they can compare it to their historic artifacts.
- pictures of "the oldest surviving counting-board ... The Salamis Tablet, ... discovered in 1846 on the island of Salamis";
- subtractive number notations in Roman Numerals and ancient Babylonian numbers;
- the striking similarity between the ancient Roman Hand Abacus and the modern Japanese Soroban;
- Roman Numerals V, L, and D, and their counterparts in ancient Greek numerals,
- "5" beads on the Roman Hand Abacus and the Japanese Soroban;
- use of five and tens complements when manipulating the Soroban, a relatively modern and practical use of subtractive notation;
- doubling and halving arithmetic of the Ancient Egyptians, et al;
- lack of a "decimal" point in cuneiform sexagesimal numbers; and
- the very large exponential number system described in Archimedes' The Sand Reckoner.
As a quick example, here's how the Romans could have found the number of years between 1997 and 2000:
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Figures 1 and 2 below show the structure of The Stephenson Abacus™. The two semicircles indicate that a number is composed of two parts, its coefficient and its exponent; like our scientific and engineering notations. The two ends of both arcs point to the positive and negative parts of the coefficient and exponent.
A base-60 number uses two horizontal lines and the space above them for each digit, so the coefficient lines are exactly enough to contain a number of the form h.hhhh, like a human hand's five digits: a thumb and four fingers. The exponent part has space for two digits; one not being enough. Perhaps the ancient Sumerians and Babylonians, and the scholars of ancient Greece, et al, used a counting-board similar to The Stephenson Abacus™ to do calculations with their base-60 place-value numbers.
A base-10 number uses one horizontal line and the space above
it for
each digit. Perhaps the ancient Romans, Greeks, Egyptians, and
Akkadians used counting-boards similar to The
Stephenson Abacus™ for their base-10 numeric
calculations; borrowing the basic structure from the base-60 board.
Numbers are represented with tokens placed on, and between, the
horizontal lines. The earliest tokens were pebbles.
"The
Roman expression for 'to calculate' is 'calculus ponere' -
literally, 'to place pebbles'. When a Roman
wished to settle accounts with someone, he would use the expression
'vocare aliquem ad calculos' - 'to call them
to the pebbles.'" In the middle ages flat coin-like
tokens called
jetons
were used. Pennies make very good tokens.
The number 123,456,789 is represented in Figure 3. To differentiate them, digits are alternately registered away from or next to the median. The digits 3, 4, 8, and 9 are represented with both positive and negative parts, which we will call subtractive form: 3 = 5 – 2, 4 = 5 – 1, 8 = 10 – 2, and 9 = 10 – 1. Use of subtractive form dramatically reduces the number of tokens needed to represent many-digit numbers, and is essential for practical arithmetic on many-digit numbers (see analysis on pages 3-4 and 8-9 in an earlier paper).
Figure 4 shows the process of counting from 0 to 8 and demonstrates converting 3 to 5 – 2, clearing positive-negative pairs of tokens (–1 + 1 = 0), and promoting two 5 tokens to one 10 token. New tokens are entered next to the bar, checked for correct entry, and then combined with existing tokens and positioned away from the bar to make room for the next entry.
Figures 5 - 8 show the steps in a series of additions of positive and negative numbers, i.e.:
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+95,641 |
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–380,276 |
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+90,375 |
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–6,813 |
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–201,073 |
Notice in Figures 6 and 7 that intermediate results don't have to be immediately readable on a digit by digit basis. To make digits readable, simply add zero pairs of tokens, e.g., –1 +1 or –5 +5, in appropriate places. An example of how to make a result readable on a digit by digit basis can be seen on page 7 here, as can a base 10 multiplication example (which includes addition and subtraction).
A multiplication in base-60 is shown here and a division here.
This Excel model can be used to add, subtract, multiply, or divide in either base-10 or base-60. Or a paper model can be used with pennies as tokens (For each abacus print 3 copies, then cut, tape, and annotate to match the figures. Do it three times to make a set of three for multiplication and division).
Here are some historical conjectures related to The Stephenson Abacus™. And here are some references with comments.
