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Monday, April 28, 2025

Count Like An Egyptian


The Bizarre Fractions of Ancient Egypt
Wrath of Math
From Wikipedia:
The Rhind Mathematical Papyrus (RMP; also designated as papyrus British Museum 10057, pBM 10058, and Brooklyn Museum 37.1784Ea-b) is one of the best known examples of ancient Egyptian mathematics.

It is one of two well-known mathematical papyri, along with the Moscow Mathematical Papyrus. The Rhind Papyrus is the larger, but younger, of the two.

In the papyrus' opening paragraphs Ahmes presents the papyrus as giving "Accurate reckoning for inquiring into things, and the knowledge of all things, mysteries ... all secrets". He continues:
This book was copied in regnal year 33, month 4 of Akhet, under the majesty of the King of Upper and Lower Egypt, Awserre, given life, from an ancient copy made in the time of the King of Upper and Lower Egypt Nimaatre. The scribe Ahmose writes this copy.
Several books and articles about the Rhind Mathematical Papyrus have been published, and a handful of these stand out. The Rhind Papyrus was published in 1923 by the English Egyptologist T. Eric Peet and contains a discussion of the text that followed Francis Llewellyn Griffith's Book I, II and III outline. Chace published a compendium in 1927–29 which included photographs of the text. A more recent overview of the Rhind Papyrus was published in 1987 by Robins and Shute.

Farther down the Wikipedia page is this image:

Ancient Egyption Units of Measurement in the Rhind Mathematical Papyrus

The image on Wikipedia contains some text, but the lines are very long which makes it difficult to read. Printing the image large enough to make the text legible requires two sheets of paper. I used Windows Paint. I had completely forgotten about this program, but it is around, at least on my Windows computer.

Anyway, I thought the text in this image ought to be converted to text, so I used OCR Online to extract the text and then edited it to correct the errors. The only words OCR had trouble with were the  highlighted words in color. Other than that it was perfect. Then I went ahead and chopped it up to make it more readable, at least in my mind. Here it is:
The present table is a concordance of ancient Egyptian units of measurement which are used throughout the Rhind Mathematical Papyrus, an ancient Egyptian document which is a record of elementary mathematics. The papyrus consists of four sections:
  1. a title page with historical information,
  2. a table of fractional calculations for 2/3 - 2/101, or the "2/n table" (where n is always odd),
  3. a much smaller table of fractional calculations for the nine fractions 1/10 - 9/10, or the "1-9/10" table, and finally
  4. a series of 91 "problems" or numbers, which are numbered from 1-87 (a modern convention imposed on the document to differentiate the problems) and include four additional items designated by moderns as 7B, 59B, 61B, and 82B.
Many of the latter problems make use of certain ancient Egyptian units of measurement, whether of length, volume, time, or otherwise, and this is what the present table summarizes. It happens that none of the 2/n table, the 1-9/10 table, or even most of the first several problems 7, 7B, 8-34 make any mention of units, and they are therefore not included in this table.
Almost all usage of units of measure is confined to the later problems in the papyrus (with some early exceptions, also listed), being the title page, problems 1-6, and problems 35-87, which include three additional items designated as 59B, 61B, and 82B.
For the title page and numbers 86-87, the context of the usage of units is not mathematical, but historical.

The units are grouped by unit type, and color-coded. From top to bottom, the unit types are:
  • length,
  • area,
  • volume (deben),
  • monetary (sha'ty),
  • trigonometric (seked),
  • food/manufacturing (pefsu), and finally
  • "foodstuff" (loaves, des-measure).
The seked is not strictly speaking a trigonometric item, but its context is so close to our modern understanding of trigonometry that we identify it with that word.
The pefsu is also a kind of derived unit of measure relating to food preparation and manufacturing.
Finally, the "loaf' is not really a standard unit of measure within the papyrus as such, but it is mentioned so frequently in related contexts that it merits its own entry. In any one problem, it can be interpreted as a measure of solid food.
Likewise, the "des-measure", mentioned in only a few problems, can be interpreted as a volume unit of liquid measure (especially in the context of food and drink) which is not immediately related to the other volume units.

Entries in black indicate that a given unit of measure is explicitly named or entailed in the problem, in the original document.
Entries in gray indicate that although the unit's word is not expressly stated in that problem, the context of the document makes clear that the unit is implicitly being used in the course of the problem's calculation, statement, etc.
Note that neighboring groups of problems often tend to entail similar units, although in some cases the units are merely strongly implied by context, as opposed to being explicitly stated in the original document.

In the Rhind Papyrus, units of a given type have precise, exact, simple relationships to one another, which conversion factors we can and therefore do easily express in modern terms, using only integers.
Although there is historical evidence that certain units of measure can be "concretely" compared with modern units, these exact specifications are not essential to reading the Rhind Papyrus as a mathematical document.
Indeed, one can read the papyrus has having an internally consistent system of units of measure, which is all that is presented in this table and explanation.
The reader is cautioned that ancient Egypt had a very long history, and that the present information about units pertains directly to the Rhind Papyrus only.
At other periods of ancient Egyptian history, certain units were taken to have different conversion factors relative to other units.

Among units of length, 1 khet = 100 cubits = 700 palms = 2800 fingers.
Among units of area, one square khet is called one setat, and 1 setat = 100 cubit strips, where one cubit strip is a rectangular strip of area being 1 cubit by 100 cubits (or any other sector of equal area).

Among units of volume, the following holds:
2 cubic cubits = 3 khar = 60 heqats = 600 hinu = 19200 ro.

Furthermore as one might expect, the somewhat redundant "hundreds/multiples" versions of the heqat and the ro can be equated with those same "base units" in the following wise:
1 hundred quadruple heqat = 2 hundred double heqats = 4 hundred heqats = 100 quadruple heqats = 200 double heqats = 400 heqats = 128000 ro = 64000 double ro = 32000 quadruple ro.

Combining these two chains of equalities, rearranging their terms, and expressing all of the units' conversion factors in the simplest terms of integers yields the following comparison among all of the standardized units of volume measurement in the Rhind Papyrus:
3 hundred quadruple heqats = 6 hundred double heqats = 12 hundred heqats = 300 quadruple heqats = 600 double heqats = 1200 heqats = 40 cubic cubits = 60 khar = 12000 hinu = 384000 ro = 192000 double ro = 96000 quadruple ro.

Among time units, since the Egyptian month is always exactly 30 days, then 6 years = 73 months = 2190 days. The remaining units, being of different types and not having simple or relevant conversion factors into other units of like type (at least as far as the papyrus itself is concerned) are therefore not expanded upon here.

More posts about fractions.

Another post about ancient mathematics: the Babylonian Plimpton 322 clay tablet. It dates from 1800 BC, so roughly the same era the Rhind Papyrus.


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