The time system in which mass balance is determined by conducting field surveys on floating calendar dates. Annual field surveys are usually carried out close to the beginning of the hydrological year. For the determination of seasonal mass balances, a survey is carried out close to the end of the accumulation season, without interpolation or extrapolation to a fixed date. The duration of the mass-balance year varies in the floating-date system. See also measurement year, stratigraphic system, fixed-date system, combined system.