Ptolemy's Table of Chords

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This Demonstration shows a reconstruction of Ptolemy's table of chords. He used 120 partes as the diameter of a circle. The chord is the red line in the semicircle. In modern terms, the table shows the values of as goes from 1/2º to 180º. The fractional parts of the chord lengths were expressed in sexagesimal (base 60) notation. After the columns for the arc and the chord (partes for integer part, for 1/60, 2 for 1/3600), a third column is labeled "sixtieths" ( for integer part, 2 for 1/60, 3 for 1/3600), calculated by . In the semicircle diagram, runs from 0 to 120 partes.


Example: .


Contributed by: Izidor Hafner (January 2016)
Open content licensed under CC BY-NC-SA



The Demonstration reconstructs the table from the Latin version called Almagestum (1515). There are a few differences of one unit between the original and the reconstruction. This makes the accuracy of the table 1/3600.


[1] Wikipedia. "Ptolemy's Table of Chords." (Jan 5, 2016)'s_table _of _chords.

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