The western European agreement for the ro-ro ferry safety reached in Stockholm in 1996 and is valid for ro-ro passenger ferries, irrespective of flag, trading regularly between two signatories, ports. According to Stockholm rules, a ferry must withstand 500 mm of water on its watertight vehicle deck when the residual freeboard in a damaged condition is below 0.3m. If the residual freeboard is above 2m, the 500 mm of water on deck is reduced to zero. The height of water is measured from the lowest point in the flooded compartment when trim and heel are taken into account. If that point is under the waterline in a damaged condition, the water height will be measured from the outside water level.