Just down from Bratch on the S&W is Botterham, which has clear instructions. Bratch is 3 individual locks without a pound you can pass in between them. The general instructions for a staircase are, for going up or down, empty bottom and full top. If going down, then there is often a weir to take any overflow if the bottom lock is full. As I said earlier, whilst some staircases may fill from a empty top, sufficient to pass the cill, if you start with a full lock, you will never be in a situation where your boat may be halfway in, and you then have to fill a double length, which could present a safety issue.