There are a few instances in the tz database where a rule is using the string "Sun<=7" rather than "Sun>=1" to mean the first Sunday in the month. I would recommend using "Sun>=1", because I think it is clearer. At least I confused "Sun<=7" with "Sun>=7" once when reading these rules, which is quite a different thing. In the africa file: Rule Algeria 1916 1919 - Oct Sun<=7 23:00s 0 - In the antarctica file: Rule ArgAQ 1967 1968 - Oct Sun<=7 0:00 1:00 S Rule ArgAQ 1968 1969 - Apr Sun<=7 0:00 0 - ... Rule ArgAQ 1974 1976 - Oct Sun<=7 0:00 1:00 S Rule ArgAQ 1975 1977 - Apr Sun<=7 0:00 0 - Regards, - Jesper 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