The "01 movement" typically refers to an in-house watch movement developed by Breitling, known as the Caliber 01. It is a mechanical movement designed and manufactured entirely by Breitling for their watches, representing the brand's own engineering and craftsmanship rather than using third-party movements

. If you meant "FS01 movement," that is a specific quartz chronograph movement made by Miyota (a division of Citizen Ltd). The Miyota FS01 is a quartz chronograph movement with three central hands (hour, minute, sweep seconds), three sub-dials, and a date window at 4 o'clock. It features parallel pushers designed for straight-sided cases, measures 23.3 mm in diameter and 4.28 mm thick, uses a battery type 377, and has no jewels. It is widely used in various watch brands and is known for reliability and ease of installation

. In summary:

• "01 movement" (Breitling Caliber 01): An in-house mechanical movement developed by Breitling

• "FS01 movement" (Miyota FS01): A Japanese quartz chronograph movement with date and 3 sub-dials, battery-powered, no jewels

If you were referring to something else by "is01 movement," please clarify, but based on available information, these are the most relevant explanations.