a quirk of the calder and hebble locks is the handspike, a length of timber shaped at one end to provide a comfortable two-handed grip. calder and hebble boaters have to carry these in addition to the more usual windlass, in order to lever open the simple lock gear which lifts the lock paddles to allow a full lock to empty or an empty one to fill. because the navigation includes river sections, locks which give access to such sections are fitted with gauge boards, which show the condition of the river using a colour-coded scheme. a green band indicates that river levels are normal, and that navigation is therefore safe. an amber band indicates that levels are higher than normal, and that extra care is required when proceeding along the river section. a red band indicates that water levels are sufficiently high that the lock has been closed, and navigation on the river is unsafe.