正筭赤負筭黑否則以邪正為異
(Jiu zhang suan shu, chapter 8 p. 175 in Guo & Liu (eds) Suan jing shi shu, Taibei 2001.)
Which means that the positive rods are red and the negative black, but adds that when this is not the case (presumably because one does not have coloured rods) "one makes a difference by means of the inclined and straight". No further explanation is given in Liu Hui's text, but In later practice (as evidenced in the 13th C.) this appears to have meant that one set out the number as usual, but with an extra rod laid diagonally across the right-hand numeral of a given number. I do not recall having heard of any excavated sets of counting-rods showing signs of having been coloured, but I have not checked this.
For completeness, perhaps one should also ask for the encoding of a set of "diagonally cancelled" rod numerals so that the second style for negative numbers could be represented.
Christopher Cullen
On 10 Jan 2004, at 15:25, Elliotte Rusty Harold wrote:
One very interesting thing I noted on the page:
Negative numbers were usually represented using distinguisable features like color. Positive rods were usually colored red while negative rods were usually colored black.
Wasn't there a really long thread not very long ago about whether color was ever a distinguishing characteristic of two otherwise identical characters?
--
Elliotte Rusty Harold
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Effective XML (Addison-Wesley, 2003)
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