cal. 324 S QA LU 24H and cal. 26-330 S QA LU 24H are the same caliber, only the name hase changed. On watchbase (click to see), ref. 5726A & ref. 5726/1A are said to be powered by caliber 324 S QA LU 24H, but on Patek's website, they are said to be powered by cal. 26-330 S QA LU 24H. Apart from the change of name, I think Patek might have made some minor improvements because the 324 caliber is sometimes mentioned as 324 S QA LU 24H/303 and the 26-330 caliber is mentioned by Patek as 26-330 S QA LU 24H/441.