In leveling, the station is the point at which the staff is held and not the position of the instrument. The operation is one of carrying forward a known level, hence the backsight is a reading taken on the staff at a known elevation and the last sight from each station is called the foresight. All other readings refer to intermediate sights. Leveling sections may be referred to bench marks or to arbitrary levels, but in all cases they must be checked either by closing on the starting point or by starting and finishing on convenient bench marks.