(in Russian, futshtok), a graduated staff that is installed at a water level measuring station in order to observe the water level in a sea, a river, or a lake. In English, water-level staffs that are used in bodies of water in which tides occur are called tide staffs; in Russian, a distinction is made between primary and secondary tide staffs.
Primary tide staffs are used to study the variation of sea level at a given location, to determine the mean sea level, and to establish a datum level for the calculation of elevations and depths. Observational data obtained with primary tide staffs are used together with data obtained by leveling between such staffs to determine differences in the levels of various seas and to study vertical motions of the earth’s surface.
Observations made with secondary tide staffs and with river and lake water-level staffs are used to solve local engineering problems that arise, for example, during the building of ports or the construction of various types of hydraulic engineering installations.
In the USSR, absolute elevations are measured from the zero point of the Kronstadt tide staff.