Four-corner method
The shapes can be memorized using a poem composed by Hu Shih, called Bihuahaoma Ge (筆畫號碼歌; Bǐhuà hàomǎ gē; 'stroke number song'), as a "memory key" to the system: 一橫二垂三點捺， 點下帶橫變零頭， 叉四插五方塊六， 七角八八小是九。 一横二垂三点捺， 点下带横变零头， 叉四插五方块六， 七角八八小是九。 Yī héng, èr chuí, sān diǎn, nà; Diǎn xià dài héng, biàn líng tóu; Chǎ sì, chā wǔ, fāng kuài liù; Qī jiǎo, bā ba, xiǎo shì jiǔ.
In the 1950s, lexicographers in the People's Republic of China changed the poem somewhat in order to avoid association with Hu Shih, who had criticized the Chinese Communist Party, although the contents remain generally unchanged.
Several other notes: There have been scores, maybe hundreds, of such numerical and alpha-numerical systems proposed or popularized (such as Lin Yutang's "Instant Index", Trindex, Head-tail, Wang An's Sanjiahaoma, Halpern); some Chinese refer to these generically as sijiaohaoma (after the original pamphlet) though this is not correct.
It was quickly adopted and popularized as a method for (among other things): The Wang Yun-wu Da Cidian of 1928 was remarkable for its time, and although the pronunciations were very much in line with today's Standard Chinese, the lack of a phonetic index diminished its overall usefulness.
By 1931, it was used extensively by the Commercial Press to index virtually all classical reference works and collections of China, such as the Pei Wen Yun Fu and Complete Library of the Four Treasuries, as well as many modern ones.
Internationally, Harvard and other universities were using the method for their book collections, and the KMT government in Nanjing seemed to have selected this numerical system as its standard.
The four-corner method was extremely popular in government education circles to promote spoken language unification until pronunciation-based systems became fashionable in the mid-1930s.
The first large-scale project to promote spoken language unification was in 1936: Wang Li's 4-volume Mandarin Phonetic System entry, Guoyu Cidian.
During the Cultural Revolution in mainland China, the four-corner method underwent a radical Third Revision during the compilation of the experimental volume of the Xiandai Hanyu Cidian, Commercial Press, Beijing, 1972.
In China today, a new version of the excellent small Xin Sijiaohaoma Cidian, soft cover from Commercial Press, Beijing, has been available since the late 1970s, updated in several new editions and printings.
The main purpose of the original four-corner system today is in doing academic research or handling large numbers of characters, terms, index cards, or names.
In China today, many famous KMT period reference books and collections with four-corner indexes are being reprinted for sale to scholars and those interested in Old Chinese language or historical studies.
