Editing Almagest (section)

==== Errors in the coordinates ====
The figure he used is based on Hipparchus' own estimate for precession, which was 1° in 100 years, instead of the correct 1° in 72 years. Dating attempts through [[proper motion]] of the stars also appear to date the actual observation to Hipparchus' time instead of Ptolemy.{{sfn|Dambis|Efremov|2000|pp=115–134}}

Many of the longitudes and latitudes have been corrupted in the various manuscripts. Most of these errors can be explained by similarities in the symbols used for different numbers. For example, the Greek letters Α and Δ were used to mean 1 and 4 respectively, but because these look similar copyists sometimes wrote the wrong one. In Arabic manuscripts, there was confusion between for example 3 and 8 (ج and ح). (At least one translator also introduced errors. [[Gerard of Cremona]], who translated an Arabic manuscript into Latin around 1175, put 300° for the latitude of several stars. He had apparently learned from [[Moors]], who [[Abjad numerals|used the letter س (sin) for 300]] (like the Hebrew [[Shin (letter)#Hebrew shin/sin|ש (shin)]]), but the manuscript he was translating came from the East, where س was used for 60, [[Hebrew numerals|like the Hebrew ס (samekh)]].){{sfn|Peters|Knobel|1915|pp=[https://archive.org/details/cu31924012300491/page/n24/mode/1up 9–14]}}

Even without the errors introduced by copyists, and even accounting for the fact that the longitudes are more appropriate for 58 AD than for 137 AD, the latitudes and longitudes are not fully accurate, with errors as great as large fractions of a degree. Some errors may be due to [[atmospheric refraction]] causing stars that are low in the sky to appear higher than where they really are.{{sfn|Peters|Knobel|1915|p=[https://archive.org/details/cu31924012300491/page/n29/mode/1up 14]}} A series of stars in [[Centaurus]] are off by a couple of degrees, including the star we call [[Alpha Centauri]]. These were probably measured by a different person or persons from the others, and in an inaccurate way.{{sfn|Peters|Knobel|1915|p=[https://archive.org/details/cu31924012300491/page/n133/mode/1up 112]}}