In the asia file, there is a rule PRC defined which is used for quite a number of timezones: Rule PRC 1986 only - May 4 0:00 1:00 D Rule PRC 1986 1991 - Sep Sun>=11 0:00 0 S Rule PRC 1987 1991 - Apr Sun>=10 0:00 1:00 D However, putting it to use in Macau seems superfluous since the PRC rule is inactive since 1991, and it is implemented for Macau only in december 1999: # Zone NAME GMTOFF RULES FORMAT [UNTIL] Zone Asia/Macau 7:34:20 - LMT 1912 8:00 Macau MO%sT 1999 Dec 20 # return to China 8:00 PRC C%sT Jesper Nørgaard Welen Email: jnorgard@Prodigy.Net.mx Project Leader (Líder de Proyecto) Software CIMMYT - Centro Internacional de Mejoramiento de Maíz y Trigo Dirección: CIMMYT Int. c/o Jesper Nørgaard Km. 45, Carretera México-Veracruz El Batán Texcoco, Edo. de México CP 56130 MEXICO Tel.: +52 (55) 58-04-20-04 ext. 1374 Fax: +52 (55) 58-04-75-58 Tel. Casa: 53-10-05-95 ó 53-10-97-78 Download the free program World Time Explorer, I made: http://www.cimmyt.org/timezone/index.htm