Method for activating an injector in a fuel injection system in an internal combustion engine

An arithmetic unit designed to activate an injector in a fuel injection system in an internal combustion engine, the fuel injection system including a plurality of injectors, and a quantity of fuel injected with the aid of an injection being a function of an activation period of the injector, the arithmetic unit to ascertain an injector-individual correction value for the activation period for the injector as a function of a pressure and a temperature of fuel to be injected, and to activate the injector in a partial lift mode under consideration of the injector-individual correction value, wherein the injector-individual correction value is ascertained based on a deviation between an actual injection period and a setpoint injection period of the injector, and wherein at a fixed pressure and a fixed temperature of the fuel to be injected, a setpoint injection quantity is varied in order to vary the setpoint injection period and to ascertain the injector-individual correction value from a dependence of the actual injection period on the setpoint injection period.