you have a block of 7 days Vacation. you can slide it 4 days either direction. However when slid it must cover a trip completely, and/or uncover a trip completely (can't slide VAC to start in the middle of a 4 day trip basically). Any trips you uncover by sliding you have to fly. with proper bidding technique, depending on seniority, you can usually turn that 7 days off into 11-18