Instead of a timer that counts down, it's a stopwatch that counts up. You focus and work until your concentration falters, then the length of the break you take is based on how long you focused. If you can get into the #flow state for 2.5 hours and you take 1/5 break time, then you take a 30 min break before starting your next session.
Otherwise known as the Flowtime Technique, lets you dive straight into a focus session until you need to take a break, with your breaks determined by how long you focus for.