9 days work
Used to be 9 working days (5 days off) every two weeks. Working days and days off can be random during the 14 days, but at least 2 off days must be in a row. Schedule normally published at least 4 weeks in advance, one week with four working days and other week with 5 working days.
Used to be possible to work a fixed work pattern/reduced time, but not sure if this is the case anymore...